[llvm] [LLVM] Refactor Autoupgrade function attributes from Module attributes. (PR #84494)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

So I think @dhoekwater and @pranavk have pointed out where the suspected reported regression may have come from in the base commit.

What happens when a module never had these module level metadata set?  There's a difference between `"sign-return-address"=0` and <nothing>.  They suspect what's happening is that modules with <nothing> are being linked against other modules, which is then setting `sign-return-address="false"` on the second module, which is now no longer being inlined.

https://github.com/llvm/llvm-project/pull/84494