OpenMP/Fortran: Add support for enter clause on declare target

OpenMP/Fortran: Add support for enter clause on declare target

Fortran version to C/C++ commit r13-797-g0ccba4ed8571c18c7015413441e971

gcc/fortran/ChangeLog:

	* dump-parse-tree.cc (show_omp_clauses): Handle OMP_LIST_ENTER.
	* gfortran.h: Add OMP_LIST_ENTER.
	* openmp.cc (enum omp_mask2, OMP_DECLARE_TARGET_CLAUSES): Add
	OMP_CLAUSE_ENTER.
	(gfc_match_omp_clauses, gfc_match_omp_declare_target,
	resolve_omp_clauses): Handle 'enter' clause.

libgomp/ChangeLog:

	* libgomp.texi (OpenMP 5.2): Mark 'enter' clause as supported.
	* testsuite/libgomp.fortran/declare-target-1.f90: Extend to test
	explicit 'to' and 'enter' clause.
	* testsuite/libgomp.fortran/declare-target-2.f90: Update accordingly.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/declare-target-2.f90: Add 'enter' clause test.
	* gfortran.dg/gomp/declare-target-4.f90: Likewise.