[clang] [clang][ThreadSafety] Check trylock function success and return types (PR #95290)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > LGTM -- that new documentation is fantastic, thank you for that!
> 
> Thank you! I hope it saves future readers some time.
> 
> I don't have write access, so feel free to merge unless we're waiting for @aaronpuchert to review :)

I'll give Aaron a chance to weigh in and land the changes on your behalf early next week if we don't hear back from him.

https://github.com/llvm/llvm-project/pull/95290