[llvm] [LLVM][rtsan] Add nonblocking Attribute and RealtimeSanitizer pass (PR #100596)

[Chris Apple via llvm-commits]

cjappl wrote:

CC for review @vitalybuka @MaskRay @Sirraide @AaronBallman  (maybe you can help suggest if someone is more appropriate in LLVM, this is my first PR in this area)

Co-author @davidtrevelyan 

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