expmed.c (expand_shift_1): Add MAY_FAIL parameter and do not assert that the result is non-zero if it is true.

	* expmed.c (expand_shift_1): Add MAY_FAIL parameter and do not assert
	that the result is non-zero if it is true.
	(maybe_expand_shift): New wrapper around expand_shift_1.
	(emit_store_flag): Call maybe_expand_shift in lieu of expand_shift.

From-SVN: r241282