[flang-commits] [flang] [flang] Change `uniqueCGIdent` separator from `.` to `_` (PR #71338)

[Fabian Mora via flang-commits]

fabianmcg wrote:

@jdoerfert just pointed out that `$` is a better option for offload identifiers as there is no possibilities of collision with user defined names -literals are never going to collide.  I see 2 options:
1. Change all separators to `$` or some other valid separator for the sake of consistency.
2. Adding a pass to change `.` in offload identifiers.

https://github.com/llvm/llvm-project/pull/71338