Fortran: With OpenACC, ignore OpenMP's cond comp sentinels

Fortran: With OpenACC, ignore OpenMP's cond comp sentinels

gcc/fortran/ChangeLog:

	PR fortran/98011
	* scanner.c (skip_free_comments, skip_fixed_comments): If only
	-fopenacc but not -fopenmp is used, ignore OpenMP's conditional
	compilation sentinels. Fix indentation, use 'else if' for readability.

gcc/testsuite/ChangeLog:

	PR fortran/98011
	* gfortran.dg/goacc/sentinel-free-form.f95:
	* gfortran.dg/goacc-gomp/fixed-1.f: New test.
	* gfortran.dg/goacc-gomp/free-1.f90: New test.
	* gfortran.dg/goacc/fixed-5.f: New test.