* target.h (targetm.vectorize.builtin_vec_perm_ok): New.
	* target-def.h (TARGET_VECTORIZE_BUILTIN_VEC_PERM_OK): New.
	* hooks.h, hooks.c (hook_bool_tree_tree_true): New.
	* tree-vect-slp.c (vect_create_mask_and_perm): Don't create
	the vector constant here...
	(vect_transform_slp_perm_load): ... do it here instead.  Validate
	that the permutation vector is implementable by the target.

From-SVN: r154665