[compiler-rt] [llvm] [AIX] PGO codegen changes for function-sections. (PR #139761)

[Wael Yehia via llvm-commits]

w2yehia wrote:

@mandlebug and I spoke offline. There's more usecases of the `.ref` assembler directive than PGO (for example the ifunc implementation will use it), so we can try generalizing the `!pgo_associated` or use the existing `!associated` metadata. Additionally, the `.rename` can also use an MD or some IR construct as it's becoming common on AIX to break down a `section` variable when it's associated to functions, so that dead functions kill the associated data variable (that has the `section` attribute) with them.

https://github.com/llvm/llvm-project/pull/139761