[flang] [llvm] [Flang][OpenMP] Add frontend support for declare variant (PR #130578)

[Tom Eccles via llvm-commits]

https://github.com/tblah commented:

Thanks for this Kiran.

The semantic restrictions on adjust_args appear to be unimplemented. I think this patch is still useful without implementing all of the semantic checks, but please update the commit message to make that clear.

https://github.com/llvm/llvm-project/pull/130578