[flang] [clang] [flang][driver] add -flang-deprecated-no-hlfir hidden option (PR #71820)

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jeanPerier wrote:

> Please could you also add testing in flang/Driver/frontend-forwarding.f90, flang/test/HLFIR/hlfir-flang.f90

Thanks for the review @tblah. I could not find flang/test/HLFIR/hlfir-flang.f90 test, did you mean flang/test/HLFIR/hlfir-**flags**.f90 (in which case it is updated in this PR already).

I added an error when -flang-deprecated-no-hlfir and -flang-experimental-hlfir are both specified and updated frontend-forwarding.f90.

https://github.com/llvm/llvm-project/pull/71820