rustc: Use rust strings for failure arguments

This avoids having to perform conversions from `*u8` to `&'static str` which can
suck in a good deal of code.

Closes #14442
Fixed deprecation warning text for mem::move_val_init and its associated comment.
rust manual: supertraits seperator is wrong
rustc: clarify warning about native deps for a staticlib.

This adjusts the "unlinked native library" warning one receives when
compiling with `crate_type="staticlib"`. The warning is just trying to
tell the user that they need to link against these libraries, but the
old text wasn't making this obvious; the new text says this explicitly.
mk: Don't build any docs with --disable-docs.
native: Ignore stdio fds with /dev/null

When spawning a process, stdio file descriptors can be configured to be ignored,
which basically means that they'll be closed. Currently this is done by
literally closing the file descriptors in the child, but this can have adverse
side effects if the child process then opens a new file descriptor, assigning it
to a stdio number.

To work around the problems of the child, this commit alters the process
spawning code to map stdio fds to /dev/null on unix (and a similar equivalent on
windows) when they are specified as being ignored. This should allow spawned
programs to have more expected behavior when opening new files.

Closes #14456
configure: Move clang's libcpp out into flag
configure: Only use -m32 on x86-* 32 bit systems
configure: setup triples on hf arm platforms
Rename UTF16Item[s] to Utf16Item[s]

According to Rust's style guide acronyms should be CamelCase.

[breaking-change]
auto merge of #14463 : SergioBenitez/rust/deprecation-fix, r=alexcrichton

The deprecation warning text for mem::move_val_init was incorrect. It should point users to `overwrite` instead of itself.
Move trait impls for primitives near trait definition

Closes #12925
std: Remove format_strbuf!()

This was only ever a transitionary macro.
Issue #13933: Remove transmute_mut from IO

The IO libraries casted self to mut so they can pass it to seek(SEEK_CUR, 0).
Fix this by introducing a private seek function that takes &self
  - of course one should be careful with it if he lacks an
    exclusive reference to self.
auto merge of #14437 : Sawyer47/rust/utf16-items, r=alexcrichton

According to Rust's style guide acronyms should be CamelCase.
Issue #13933: Remove transmute_mut from Arc

directly use the internal pointer instead.
auto merge of #13738 : buttslol/rust/armv7-support, r=alexcrichton

This was required to get ./configure to work on my armv7 test machine.

I haven't found anything sane to feature gate `hf` on that's pokable from the context of the configure script.

It also seems that gcc doesn't work on armv7 by default (rust wants to pass it `-m32` which isn't supported), would it be preferential to make the default `--enable-clang` on arm, or remove the `-m32` flag on that platform?
auto merge of #14464 : Sawyer47/rust/issue-12925, r=alexcrichton

This is an attempt of fixing #12925.

This PR moves almost all trait implementations for primitive types ((), bool, char, i*, u*, f*) near trait definitions. Only Float trait implementations weren't moved because they heavily rely on constants defined in f32.rs and f64.rs.

Some trait implementations had cfg(not(test)) attribute. I suspect it's because of issue 2912.
Still, someone who knows the problem better should probably check this code.

Closes #12925
Silence warning in RefCell test suite
Add AST node for pattern macros