OpenACC 2.6 deep copy: libgomp parts

	include/
	* gomp-constants.h (GOMP_MAP_FLAG_SPECIAL_4, GOMP_MAP_DEEP_COPY):
	Define.
	(gomp_map_kind): Add GOMP_MAP_ATTACH, GOMP_MAP_DETACH,
	GOMP_MAP_FORCE_DETACH.

	libgomp/
	* libgomp.h (struct target_var_desc): Add do_detach flag.
	* oacc-init.c (acc_shutdown_1): Free aux block if present.
	* oacc-mem.c (find_group_last): Add SIZES parameter. Support
	struct components.  Tidy up and add some new checks.
	(goacc_enter_data_internal): Update call to find_group_last.
	(goacc_exit_data_internal): Support detach operations and
	GOMP_MAP_STRUCT.
	(GOACC_enter_exit_data): Handle initial GOMP_MAP_STRUCT or
	GOMP_MAP_FORCE_PRESENT in finalization detection code.  Handle
	attach/detach in enter/exit data detection code.
	* target.c (gomp_map_vars_existing): Initialise do_detach field of
	tgt_var_desc.
	(gomp_map_vars_internal): Support attach.
	(gomp_unmap_vars_internal): Support detach.

From-SVN: r279625