[llvm] [LLVM][rtsan] Add LLVM nosanitize_realtime attribute (PR #105447)

[Chris Apple via llvm-commits]

cjappl wrote:

@pcc - I think I'll submit this as is tomorrow morning PST following vitaly's approval. If you want to continue talking it over, I could I file a discourse thread and ping the interested parties (vitaly, nikic, you, me, people from the original RFC thread) and we can hash out if one approach is better than the other. If doing it in the frontend is best, I can submit a patch reverting any of the LLVM and putting it in clang in one swoop to maintain the functionality we have built so far.

If you don't feel strongly, I can just keep trucking with this approach! I will add you to the transform review (following this) if you're amenable :) 

https://github.com/llvm/llvm-project/pull/105447