Repository: rust
Issue: `x.py test` does not handle spaces in filenames for `build-aux` files
Labels: A-testsuite,T-bootstrap,C-bug,A-contributor-roadblock

I tried this command: `x test "src\test\rustdoc\intra-doc\pub-use.rs"`.

I expected to see this happen: The test passes.

Instead, this happened:
```
command: PATH="C:\Users\Joshua Nelson\src\rust\build\x86_64-pc-windows-msvc\stage2\bin;C:\Program Files (x86)\Windows Kits\10\bin\x64;C:\Program Files (x86)\Windows Kits\10\bin\10.0.19041.0\x64;C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.28.29910\bin\HostX64\x64;C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.28.29910\bin\HostX64\x64;C:\Users\Joshua Nelson\src\rust\build\x86_64-pc-windows-msvc\stage0-bootstrap-tools\x86_64-pc-windows-msvc\release\deps;C:\Users\Joshua Nelson\src\rust\build\x86_64-pc-windows-msvc\stage0\bin;C:\Users\Joshua Nelson\bin;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\local\bin;C:\Program Files\Git\usr\bin;C:\Program Files\Git\usr\bin;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\bin;C:\Users\Joshua Nelson\bin;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\Program Files (x86)\Intel\iCLS Client;C:\Program Files\Intel\iCLS Client;C:\windows\system32;C:\windows;C:\windows\System32\Wbem;C:\windows\System32\WindowsPowerShell\v1.0;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0;C:\WINDOWS\System32\OpenSSH;C:\Program Files\Intel\WiFi\bin;C:\Program Files\Common Files\Intel\WirelessCommon;C:\Program Files\Git\cmd;C:\Users\Joshua Nelson\.cargo\bin;C:\Users\Joshua Nelson\AppData\Local\Microsoft\WindowsApps;C:\Program Files\Intel\WiFi\bin;C:\Program Files\Common Files\Intel\WirelessCommon;C:\Users\Joshua Nelson\AppData\Local\Programs\Microsoft VS Code\bin;C:\Users\Joshua Nelson\AppData\Local\Programs\Python\Python39;C:\Program Files\Git\usr\bin\vendor_perl;C:\Program Files\Git\usr\bin\core_perl" "C:\\Users\\Joshua Nelson\\src\\rust\\build\\x86_64-pc-windows-msvc\\stage2\\bin\\rustc.exe" "C:\\Users\\Joshua Nelson\\src\\rust\\src/test\\rustdoc\\intra-doc\\auxiliary\\intra-link-pub-use.rs" "-Zthreads=1" "--target=x86_64-pc-windows-msvc" "-C" "prefer-dynamic" "--out-dir" "C:\\Users\\Joshua Nelson\\src\\rust\\build\\x86_64-pc-windows-msvc\\test\\rustdoc\\intra-doc\\pub-use\\auxiliary" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=C:\\Users\\Joshua" "Nelson\\src\\rust\\build\\x86_64-pc-windows-msvc\\native\\rust-test-helpers" "--crate-type" "dylib" "-L" "C:\\Users\\Joshua Nelson\\src\\rust\\build\\x86_64-pc-windows-msvc\\test\\rustdoc\\intra-doc\\pub-use\\auxiliary"
------------------------------------------
stderr:
------------------------------------------
error: multiple input filenames provided (first two filenames are `C:\Users\Joshua Nelson\src\rust\src/test\rustdoc\intra-doc\auxiliary\intra-link-pub-use.rs` and `Nelson\src\rust\build\x86_64-pc-windows-msvc\native\rust-test-helpers`)
```

I think this is because RUSTFLAGS can't handle spaces: https://github.com/rust-lang/rust/blob/5f10d310f475b3ba583b9c590b8d19f6c2fde28f/src/bootstrap/test.rs#L1267
docs.rs worked around this with `-Zconfig`, maybe bootstrap can do the same? https://github.com/rust-lang/docs.rs/pull/1057

### Meta

`$ git merge-base origin/master HEAD`: 3e99439f4dacc8ba0d2ca48d221694362d587927