[clang] [compiler-rt] [llvm] [clang][llvm][rtsan] Introduce RealtimeSanitizer clang codegen, llvm attributes (PR #100120)

[Chris Apple via cfe-commits]

cjappl wrote:

Closing in favor of these two reviews to begin with, a 3rd will be added with the lit test components after these are merged:

1. Fixing unit test intermittent failure on mac: https://github.com/llvm/llvm-project/pull/100188
2. clang codegen component https://github.com/llvm/llvm-project/pull/100192
3. (NOT POSTED YET) Initial lit tests and re-enabling our instrumented unit tests from this review

https://github.com/llvm/llvm-project/pull/100120