[clang] [clang][rtsan] Introduce realtime sanitizer codegen and driver (PR #102622)

[Chris Apple via cfe-commits]

cjappl wrote:

I was not able to figure out a way to separate the CodeGen from the driver, seeing as the codegen only happens when the sanitizer is enabled. This means to write unit tests for the CodeGen, I needed the -fsanitize=realtime flag. If someone has advice on how to get around this problem I'm more than happy to break this up if it is too big!

https://github.com/llvm/llvm-project/pull/102622