[clang] [compiler-rt] [compiler-rt] Realtime Sanitizer: Introduce Realtime Sanitizer (RTSan) backend (PR #92460)

[Chris Apple via cfe-commits]

cjappl wrote:

> clangDriver changes are usually the last. The expectation is that if -fsanitize=realtime does not return an error, there should be some basic functionality.

Thanks for the feedback @MaskRay . I removed all of the clang components of this review, leaving only the compiler-rt components. We will re-introduce the clang changes in a future review.

In the meantime, I commented out compilation of our unit tests that required the -fsanitize flag, let me know if you'd prefer to see them removed until later. These unit tests are paired with the code introduced here, so I think at least by subject it makes sense to introduce them here, even if they are briefly not being compiled.

https://github.com/llvm/llvm-project/pull/92460