Fortran - Improve OpenMP/OpenACC diagnostic

Fortran - Improve OpenMP/OpenACC diagnostic

	Backported from mainline.

        gcc/fortran/
        * match.h (gfc_match_omp_eos_error): Renamed from gfc_match_omp_eos.
        * openmp.c (gfc_match_omp_eos): Make static.
        (gfc_match_omp_eos_error): New.
        * parse.c (matchs, matchdo, matchds): Do as done for 'matcho' -
        if error occurred after OpenMP/OpenACC directive matched, do not
        try other directives.
        (decode_oacc_directive, decode_omp_directive): Call new function
        instead.

        testsuite/
        * gfortran.dg/goacc/continuation-free-form.f95: Update dg-error.

(cherry picked from openacc-gcc-9-branch commit
55858edc1aab472abe850a74b22302dcfa735715)