openacc: Fix lowering for derived-type mappings through array elements

openacc: Fix lowering for derived-type mappings through array elements

This patch fixes lowering of derived-type mappings which select elements
of arrays of derived types, and similar. These would previously lead
to ICEs.

With this change, OpenACC directives can pass through constructs that
are no longer recognized by the gimplifier, hence alterations are needed
there also.

gcc/fortran/
	* trans-openmp.c (gfc_trans_omp_clauses): Handle element selection
	for arrays of derived types.

gcc/
	* gimplify.c (gimplify_scan_omp_clauses): Handle ATTACH_DETACH
	for non-decls.

gcc/testsuite/
	* gfortran.dg/goacc/array-with-dt-1.f90: New test.
	* gfortran.dg/goacc/array-with-dt-3.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-4.f90: Likewise.
	* gfortran.dg/goacc/array-with-dt-5.f90: Likewise.
	* gfortran.dg/goacc/derived-chartypes-1.f90: Re-enable test.
	* gfortran.dg/goacc/derived-chartypes-2.f90: Likewise.
	* gfortran.dg/goacc/derived-classtypes-1.f95: Uncomment
	previously-broken directives.

libgomp/
	* testsuite/libgomp.oacc-fortran/derivedtypes-arrays-1.f90: New test.
	* testsuite/libgomp.oacc-fortran/update-dt-array.f90: Likewise.