[Flang][OpenMP][Feature Request] accept `-fno-openmp`

[k-arrows]

I think flang-new should accept -fno-openmp. Clang and Gfortran accept this.

$ clang -fno-openmp test.c
$ gfortran -fno-openmp test.f90
$ flang-new -fno-openmp test.f90
flang-new: error: unknown argument: '-fno-openmp'

But I think the priority is not so high because the intended behavior is achieved by not specifying -fopenmp.

[llvmbot]

@llvm/issue-subscribers-flang-driver

Author: None (k-arrows)

I think flang-new should accept `-fno-openmp`. Clang and Gfortran accept this. ```console $ clang -fno-openmp test.c $ gfortran -fno-openmp test.f90 $ flang-new -fno-openmp test.f90 flang-new: error: unknown argument: '-fno-openmp' ```

But I think the priority is not so high because the intended behavior is achieved by not specifying -fopenmp.