[llvm] [rtsan] Handle attributed IR function declarations (PR #169577)

[Chris Apple via llvm-commits]

https://github.com/cjappl approved this pull request.

Approved as written! I lean slightly to breaking the NFC into another commit but not strongly enough to block based on it

Thanks for investigating the other sanitizers. Looks like there is good precedence for this type of check


https://github.com/llvm/llvm-project/pull/169577