[llvm] [llvm/Support] Make `llvm::sys::RWMutex` Lockable (PR #90667)

[Jonas Devlieghere via llvm-commits]

https://github.com/JDevlieghere requested changes to this pull request.

It looks like this is trying to implement something like `is_locked`. `try_lock` has fairly well defined semantics for `std::mutex` and `pthreads`. In both cases this acquires the lock if it succeeds. Our implementation shouldn't behave differently. 

https://github.com/llvm/llvm-project/pull/90667