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

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

> This matches what our users do in practice: since `used` doesn't survive the AIX link, the accepted workaround downstream is marking each string `__attribute__((visibility("protected"))) __attribute__((weak))`.

This workaround is not generally applicable. It relies on the variable names being unique, across the inputs to a link-edit/bind operation, for each unique string value.

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