[flang-commits] [flang] [flang][NFC] Fix header guards (PR #85801)

[Tarun Prabhu via flang-commits]

tarunprabhu wrote:

I can switch the prefixes (back) to `LLVM_FLANG_`, but those would be the only instances of `LLVM_FLANG_` in the whole repo. Everything else uses `FORTRAN_` and that is also consistent with the namespace in use. I'll let others chime in and edit the patch accordingly.

https://github.com/llvm/llvm-project/pull/85801