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

[Alex Langford via llvm-commits]

https://github.com/bulbazord commented:

Can't say I know a lot about this code, but your explanations and comments make sense to me. I left one suggestion but I'll leave the final approval to somebody more knowledgable.

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