[compiler-rt] Fix sendmmsg and recvmmsg rtsan interceptor for MUSL (PR #123907)

[Chris Apple via llvm-commits]

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

LGTM thank you!!

This is just musings doesn't affect this review - I wonder if there is a better way to organize all the differences of signatures across versions/libcs/OSs. One that is more readable or maintainable.

As we continue adding interceptors we may want to re-organize in some way

https://github.com/llvm/llvm-project/pull/123907