[clang] [llvm] Disentangle DISubprogram ODR type method uniquing from metadata uniquing (PR #217042)

[Orlando Cazalet-Hyams via cfe-commits]

https://github.com/OCHyams commented:

Thanks for the review @dzhidzhoev ! You're right about the placeholder situation. I've given fixing it a go - it seems to work, but it's not very pretty

There seems to now be a disagreement in metadata order in `llvm/test/Assembler/dicompositetype-members.ll`, which I'm looking into. I thought it would be good to get the fix up in the meantime, in case you have opinions on the shape of it

https://github.com/llvm/llvm-project/pull/217042