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The tracking issue has been replaced by one with mentoring instructions.

…tthewjasper

Rust 2018: NLL migrate mode => hard error

As per decision on a language team meeting as described in rust-lang#63565 (comment), we refuse to downgrade NLL errors, that AST borrowck accepts, into warnings and keep them as hard errors.

cc @rust-lang/lang
cc @rust-lang/wg-compiler-nll

… r=sfackler

Add missing examples for Option type

cc @rust-lang/docs

…xcrichton

Remove no-prefer-dynamic from valgrind tests

This seems to be working locally.

Resolves rust-lang#31968

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The tracking issue has been replaced by one with mentoring instructions (rust-lang#64205).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