Repository: rust
Issue: Bad value for `target-cpu` has spammy and confusing error output
Labels: A-LLVM,A-diagnostics,T-compiler,D-verbose,A-target-feature

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This same error spam reproduces if using an intentionally bad target, like `RUSTFLAGS='-C target-cpu=xxx-todo'`.

`fn main() {}

on x86_64 macOS.

compiling with:

```console
rustc main.rs -Ctarget-cpu=cortex-a75
```

The current output is:

```
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
<cut>
```

<details>

```console
$ rustc main.rs -Ctarget-cpu=cortex-a75
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
error: could not compile `bitflags`
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
libc++abi: Pure virtual function called!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
'cortex-a75' is not a recognized processor for this target (ignoring processor)
LLVM ERROR: 64-bit code requested on a subtarget that doesn't support it!
error: build failed
```

</details>

<!-- The following is not always necessary. -->
Ideally the output should look like:

something less spammy.

<!--
If the problem is not self-explanatory, please provide a rationale for the
change.
-->

<!--
If dramatically different output is caused by small changes, consider also
adding them here.

If you're using the stable version of the compiler, you should also check if the
bug also exists in the beta or nightly versions. The output might also be
different depending on the Edition.
-->

## meta

```console
$ rustc -Vv
rustc 1.56.1 (59eed8a2a 2021-11-01)
binary: rustc
commit-hash: 59eed8a2aac0230a8b53e89d4e99d55912ba6b35
commit-date: 2021-11-01
host: x86_64-apple-darwin
release: 1.56.1
LLVM version: 13.0.0
```

### background

I accidentally copy-and-pasted the `RUSTFLAGS` example for `-C target-cpu=` from https://rust-lang.github.io/packed_simd/perf-guide/target-feature/rustflags.html#target-cpu in an attempt to compile for `target-cpu=native`.

It looks like x86_64 Darwin doesn't like the `cortex-a75` CPU type and I got a lot of unexpected output before the build errored out in LLVM.