[llvm] [LLVM][rtsan] Add RealtimeSanitizer transform pass (PR #101232)

[Chris Apple via llvm-commits]

cjappl wrote:

@MaskRay @vitalybuka could I get a merge when you get a chance?

Since your last review I:
* Rebased on latest main
* changed the attribute name to be `sanitize_realtime` which was the change in my previous review. Everything else is the same as when you reviewed it.

Test being green shows that change took and everything is working as intended!

Thanks as always.

https://github.com/llvm/llvm-project/pull/101232