[clang] [flang] [flang] Align `-x` language modes with `gfortran` (PR #130268)

[Iñaki Amatria Barral via cfe-commits]

inaki-amatria wrote:

> This LGTM now when @tarunprabhu is happy, thanks for seeing this through despite my lengthy comments!

Thank you for the quick review, David! I also appreciate your patience with my lengthy comments. I was so caught up in the fixed-form assumption that I failed to realize that reverting the patch I had intended to undo in the previous PR would introduce a regression on your side. I truly appreciate your time and insights!

> This isn't to hold up this patch, but as a separate thought: I wonder if there's even any reason to have `types::TY_PP_Fortran` and `types::TY_Fortran`? Do we ever actually treat them differently..? It seems we always decide whether to preprocess or not based on other criteria

As for your separate thought: I agree that this part of the code might benefit from a second look.

https://github.com/llvm/llvm-project/pull/130268