Avoid bool pattern for vect_extern_defs

Avoid bool pattern for vect_extern_defs

The following avoids applying the new bool pattern for binary bitwise
ops when the wrongly typed operand is external or constant as we
cannot handle in-loop conversions of externs.

	* tree-vect-patterns.cc (integer_type_for_mask): Add optional
	output dt argument.
	(vect_recog_bool_pattern): Make sure to not apply the bitwise
	binary pattern to an external operand.