Feature: Add `-fsanitize=address` for `x86_64-unknown-linux-gnuasan`

[kamulos]

I think it could make sense to have cc automatically set -fsanitize=address, when the new target x86_64-unknown-linux-gnuasan is selected in Rust. This would make enabling ASAN in mixed code bases incredibly easy. And I think this would be what the user intends in every case when selecting the target.

I wanted to open a PR for this, but I am too unfamiliar with the code base to do it properly

[madsmtm]

Hmm, there's a cfg!(sanitize = "address"), right? This should be exposed to us in CARGO_CFG_SANITIZE, so I think all we'd need to do would be to read that, and pass the corresponding -fsanitize=... flags to the C compiler.

[kamulos]

Just tried it, that seems to be set for x86_64-unknown-linux-gnuasan as well as RUSTFLAGS="-Z sanitizer=address" 😊

If nobody is faster than me, I will open a PR tomorrow