We never allowed the warnings, only made them not denied.

Previously the build would take the presence of the LLVM_CONFIG envvar to
mean that the sanitizers should be built, but this is a common envvar that
could be set for reasons unrelated to the rustc sanitizers.

This commit adds a new envvar RUSTC_BUILD_SANITIZERS and uses it instead.

This moves the two methods from the `EmitterWriter` impl to trait
default methods in the `Emitter` trait so that they can be re-used by
the `AnnotateSnippetEmitterWriter`.

Closes rust-lang#61810

The tracking issue has been replaced by one with mentoring instructions.

…xcrichton

Remove no-prefer-dynamic from valgrind tests

This seems to be working locally.

Resolves rust-lang#31968

…used, r=petrochenkov

compiletest: disable -Aunused for run-pass tests

Disabled the flag, but that led to quite a bit of fall out -- I think most of it is benign but I've not investigated thoroughly.

r? @petrochenkov

…ark-Simulacrum

Fix regex replacement in theme detection

Fixes rust-lang#64061.

This is sadly a lot of bad luck: after making the changes and re-build the docs, I just forgot to force reload the page. Hence having the old (working) version with two replacements instead of the failing regex. Sorry again about that...

cc @fenhl
r? @Mark-Simulacrum

…crichton

Ensure edition lints and internal lints are enabled with deny-warnings=false

Previously we only passed the deny command line flags if deny-warnings was enabled, but now we either pass -W... or -D... for each of the flags as appropriate.

This is also a breaking change to x.py as it changes `--warnings=allow` to `--warnings=warn` which is what that flag actually did; we don't have an allow warnings mode.

Better way of conditioning the sanitizer builds

Previously the build would take the presence of the LLVM_CONFIG envvar to
mean that the sanitizers should be built, but this is a common envvar that
could be set for reasons unrelated to the rustc sanitizers.

This commit adds a new envvar RUSTC_BUILD_SANITIZERS and uses it instead.

This PR or similar will be necessary in order to work correctly with rust-lang/compiler-builtins#296

annotate-snippet emitter: Deal with multispans from macros, too

This moves the two methods from the `EmitterWriter` impl to trait
default methods in the `Emitter` trait so that they can be re-used by
the `AnnotateSnippetEmitterWriter`.

r? @estebank

Closes rust-lang#61810

Fixed grammar/style in some error messages

Factored out from hacking on rustc for work on the REPL.

r? @Centril

annotate-snippet emitter: Update an issue number

The tracking issue has been replaced by one with mentoring instructions (rust-lang#64205).

it's more pythonic to use 'is not None' in python files