[clang] [llvm] [Clang][AIX] Add -mloadtime-comment-vars flag to preserve identifying variables (PR #187986)

[Tony Varghese via cfe-commits]

tonykuttai wrote:

> I think it's better to have a single representation in IR for the two FE interfaces, and have the lowering pass handle one representation.

Thanks Wael. I have updated the design in #178184 and which means we dont need any changes to the `LowerCommentStringPass` as it will work soley based on the `loadtime_comment` metadata. 

https://github.com/llvm/llvm-project/pull/187986