[llvm] [LLVM][rtsan] Add sanitize_realtime attribute for the realtime sanitizer (PR #100596)

[Chris Apple via llvm-commits]

cjappl wrote:

@nikic based on your suggestions, I decided to update this to the attribute `sanitize_realtime`. Let me know if this works for you or you want to see other changes.

https://github.com/llvm/llvm-project/pull/100596