OpenMP: Handle descriptors in target's firstprivate [PR104949]

For allocatable/pointer arrays, a firstprivate to a device
not only needs to privatize the descriptor but also the actual
data. This is implemented as:
  firstprivate(x) firstprivate(x.data) attach(x [bias: &x.data-&x)
where the address of x in device memory is saved in hostaddrs[i]
by libgomp and the middle end actually passes hostaddrs[i]' to
attach.

As side effect, has_device_addr(array_desc) had to be changed:
before, it was converted to firstprivate in the front end; now
it is handled in omp-low.cc as has_device_addr requires a shallow
firstprivate (not touching the data pointer) while the normal
firstprivate requires (now) a deep firstprivate.

gcc/fortran/ChangeLog:

	PR fortran/104949
	* f95-lang.cc (LANG_HOOKS_OMP_ARRAY_SIZE): Redefine.
	* trans-openmp.cc (gfc_omp_array_size): New.
	(gfc_trans_omp_variable_list): Never turn has_device_addr
	to firstprivate.
	* trans.h (gfc_omp_array_size): New.

gcc/ChangeLog:

	PR fortran/104949
	* langhooks-def.h (lhd_omp_array_size): New.
	(LANG_HOOKS_OMP_ARRAY_SIZE): Define.
	(LANG_HOOKS_DECLS): Add it.
	* langhooks.cc (lhd_omp_array_size): New.
	* langhooks.h (struct lang_hooks_for_decls): Add hook.
	* omp-low.cc (scan_sharing_clauses, lower_omp_target):
	Handle GOMP_MAP_FIRSTPRIVATE for array descriptors.

libgomp/ChangeLog:

	PR fortran/104949
	* target.c (gomp_map_vars_internal, copy_firstprivate_data):
	Support attach for GOMP_MAP_FIRSTPRIVATE.
	* testsuite/libgomp.fortran/target-firstprivate-1.f90: New test.
	* testsuite/libgomp.fortran/target-firstprivate-2.f90: New test.
	* testsuite/libgomp.fortran/target-firstprivate-3.f90: New test.