[llvm] [DebugInfo] Add a specification attribute to LLVM DebugInfo (PR #115362)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie approved this pull request.

Could be worth splitting this into smaller steps - asm reading/writing, separate from the functional change in LLVM AsmPrinter, etc. 

I still have reservations about using DW_AT_specification for this, but DWARF is permissive and all that, so if it's what you folks want to use for Swift, guess that's fine.

https://github.com/llvm/llvm-project/pull/115362