Split return functionality of get_non_stale_global_range.

Split return functionality of get_non_stale_global_range.

Get_non_stale_global_range returns true only when there is a cache entry that
is not out of date.  Change it so that it returns true if there was a cache
value, but return the temporal comparison result in an auxiallary flag.

	* gimple-range-cache.cc (ranger_cache::get_global_range): Always
	return a range, return if it came from the cache or not.
	(get_non_stale_global_range): Rename to get_global_range, and return
	the temporal state in a flag.
	* gimple-range-cache.h (get_non_stale_global_range): Rename and adjust.
	* gimple-range.cc (gimple_ranger::range_of_expr): No need to query
	get_global_range.
	(gimple_ranger::range_of_stmt): Adjust for global cache temporal state
	returned in a flag.