Sanitizer support allow-list should not be baked into the compiler (outside of the built-in targets)

[nagisa]

We have code such as this in our codebase that encodes an allow-list of targets that support for a given sanitizer:

rust/compiler/rustc_session/src/session.rs

Line 1541 in 5605b5d

const ASAN_SUPPORTED_TARGETS: &[&str] = &[

Instead, the code should be adjusted to only encode such support table in the target definitions. The compiler otherwise should be pretty agnostic to both the list of available sanitizers (outside of the backend) and targets that support it.