[OpenACC] In 'libgomp/target.c:gomp_to_device_kind_p', handle 'GOMP_MAP_FORCE_FROM' like 'GOMP_MAP_FROM'

Fix oversight from r254194 "Coalesce host to device transfers in libgomp".

	libgomp/
	* target.c (gomp_to_device_kind_p): Handle 'GOMP_MAP_FORCE_FROM'
	like 'GOMP_MAP_FROM'.

From-SVN: r279533