[llvm] [Dwarf][Transforms] Add dwarf support when func signature changed (PR #127855)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Could we use only the `DW_AT_calling_convention` with `DW_CC_nocall` for this? (without the nuance/differentiation between return values and parameters, and lets us use the standard feature)

https://github.com/llvm/llvm-project/pull/127855