[llvm] [DebugInfo] Make DISubprogram's hashing always produce the same result (PR #90770)

[Augusto Noronha via llvm-commits]

augusto2112 wrote:

> What about cases where the mangled name is not included - I guess, for subprogram definitions, maybe that only comes up in something like C?

@dwblaikie In that case the hash would be based off of the other fields (Name, File, Type, Line), so it should still be a good enough hashing function.

https://github.com/llvm/llvm-project/pull/90770