Allow `!` as the return type of proc/closure literals

Fixes #13490.
Change rustc to say `array` instead of `vector`
core: Make TwoWaySearcher reset its prefix memory when shifting by byteset

Closes #16878.
Add many comments to TwoWaySearcher.
Add some tests for closures that return `!`
Add unnecessary_import_braces lint.

The lint checks any unnecessary braces around one imported item like
`use std::num::{abs};`.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
mk: Fix defs for i686-w64-mingw32
Updated jemalloc
Remove build system support for i686-pc-mingw32 triple in favor if i686-w64-mingw32
Fix bad error message copypasta
Add a Rust string ostream for LLVM
Add -C remark for LLVM optimization remarks

Fixes #17116.
Remove unused, unsound method on StrInterner

The string slices returned by `get_ref` can actually be
invalidated by calling `clear`.  Since this method is unused,
it is easiest to simply remove it.

Closes #17181
Improve memory usage of libsyntax
Replaces some usage of `.to_string()` with `.into_string()`

Signed-off-by: Peter Atashian <retep998@gmail.com>
doc: that felt like it needed a stronger break than what comma provides

Remove trailing whitespace while at it
These two lines are actually three.
Move info into individual modules.
Remove container guide.

This isn't really what guides are for, this information belongs in the
module-level docs.

Fixes #9314.
Fix issue #17216

The cleanup scope of for loop bindings should translated when
popped to ensure resources are not leaked.
Properly implement Show for EnumSet