[PATCH] OpenMP: Improve Fortran metadirective diagnostics [PR107067]

[PATCH] OpenMP: Improve Fortran metadirective diagnostics [PR107067]

The Fortran front end was giving an ICE instead of a user-friendly
diagnostic when variants of a metadirective variant had different
statement associations.  The particular test case reported in the issue
also involved invalid placement of the "omp end metadirective" which
was not being diagnosed either.

gcc/fortran/ChangeLog
	PR middle-end/107067
	* parse.cc (parse_omp_do): Diagnose missing "OMP END METADIRECTIVE"
	after loop.
	(parse_omp_structured_block): Likewise for strictly structured block.
	(parse_omp_metadirective_body): Use better test for variants ending
	at different places.  Issue a user diagnostic at the end if any
	were inconsistent, instead of calling gcc_assert.

gcc/testsuite/ChangeLog
	PR middle-end/107067
	* gfortran.dg/gomp/metadirective-11.f90: Remove the dg-ice, update
	for current behavior, and add more tests to exercise the new error
	code.