[compiler-rt] [rtsan] Added mmap and shm interceptors (PR #114862)

[Chris Apple via llvm-commits]

cjappl wrote:

As a meta note to @fmayer and @davidtrevelyan, I'm going to start doing a little work each week trying to fill out the most obvious missing holes in our interceptors.

I figure a small/focused-ish PR in the same area is the way to go (instead of one per interceptor, which seems like a lot of overhead), but I'm open to any feedback or suggestions.

This one is in the broad umbrella "virtual memory". The next one is "sockets" (as we are missing some things like connect, bind, etc)

https://github.com/llvm/llvm-project/pull/114862