[llvm] [Support] Optimize signal handling file removal code (PR #173586)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I've read the existing comments. I think llvm::sys::RemoveFileOnSignal and llvm::sys::DontRemoveFileOnSignal are almost always paired (sys::fs::TempFile, OnDiskOutputFile, LockFileManager) through RAII wrappers, so bumping the time complexity of insert() to O(N) isn't an issue since erase() is already O(N).

https://github.com/llvm/llvm-project/pull/173586