[compiler-rt] [rtsan] Add I/O multiplexing interceptors (PR #115227)

[Chris Apple via llvm-commits]

cjappl wrote:

I'm going to submit this later today and do a post-commit review - I think these additions of new interceptors are relatively uncontroversial, and have good test coverage.

I'll likely follow with more interceptors in the coming days/weeks where I'll do a similar thing, I'll try to draw everyones attention to any interesting bits, but I hope they are as straightforward as this one 

https://github.com/llvm/llvm-project/pull/115227