OpenMP/Fortran: Reject not strictly nested target -> teams [PR110725, PR71065]

OpenMP requires: "If a teams region is nested inside a target region, the
corresponding target construct must not contain any statements, declarations
or directives outside of the corresponding teams construct."

This commit checks now for this restriction.

	PR fortran/110725
	PR middle-end/71065

gcc/fortran/ChangeLog:

	* gfortran.h (gfc_omp_clauses): Add contains_teams_construct.
	* openmp.cc (resolve_omp_target): New; check for teams nesting.
	(gfc_resolve_omp_directive): Call it.
	* parse.cc (decode_omp_directive): Set contains_teams_construct
	on enclosing ST_OMP_TARGET.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/pr99226.f90: Update dg-error.
	* gfortran.dg/gomp/teams-5.f90: New test.