[clang] [clang][rtsan] Introduce realtime sanitizer clang codegen and -fsanitize flag (PR #100192)

[Chris Apple via cfe-commits]

cjappl wrote:

Thanks to the feedback from @MaskRay and @vitalybuka , closing in favor of doing this processing in LLVM.  (PR: https://github.com/llvm/llvm-project/pull/100596)

The clang driver changes will come after that is merged! Appreciate all the reviews setting us on the right path.

https://github.com/llvm/llvm-project/pull/100192