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

[via llvm-commits]

pcc wrote:

So do you really need the LLVM attributes then? Would it not suffice to have Clang IRGen add the calls to `__rtsan_bypass_on/off` and `__rtsan_realtime_enter/exit` based on the Clang attributes? The other sanitizers have passes because they need to be able to operate on arbitrary instructions in each function after optimization, but if RTSan only needs to affect function entry/exit then that seems much more straightforwardly accomplished in the frontend.

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