In <rust-lang#126922>, the
`binary_asm_labels` lint was added which flags labels such as `0:` and
`1:`. Before that change, LLVM was giving a confusing error on
x86/x86_64 because of an incorrect interpretation.

However, targets other than x86 and x86_64 never had the error message
and have not been a problem. This means that the lint was causing code
that previously worked to start failing (e.g. `compiler_builtins`),
rather than only providing a more clear messages where there has always
been an error.

Adjust the lint to only fire on x86 and x86_64 assembly to avoid this
regression.

The link pointed to a closed issue. Create a new one and point the link
to it.

Also add a help message to hint what change the user could make.

Fixes: rust-lang#127821

Disable a test that now only passes on x86 and make the link point to
the new (open) LLVM bug.