Make ISEL used internal functions const/nothrow where appropriate

Both .VEC_SET and .VEC_EXTACT and the various .VCOND internal functions
are operating on registers only and they are not supposed to raise
any exceptions.  The following makes them const/nothrow.  I've
verified this avoids useless SSA updates in ISEL.

	* internal-fn.def (VCOND, VCONDU, VCONDEQ, VCOND_MASK,
	VEC_SET, VEC_EXTRACT): Make ECF_CONST | ECF_NOTHROW.

gcc/internal-fn.def

@@ -209,13 +209,15 @@ DEF_INTERNAL_OPTAB_FN (STORE_LANES, ECF_CONST, vec_store_lanes, store_lanes)
 DEF_INTERNAL_OPTAB_FN (MASK_STORE_LANES, 0,
 		       vec_mask_store_lanes, mask_store_lanes)
 
-DEF_INTERNAL_OPTAB_FN (VCOND, 0, vcond, vec_cond)
-DEF_INTERNAL_OPTAB_FN (VCONDU, 0, vcondu, vec_cond)
-DEF_INTERNAL_OPTAB_FN (VCONDEQ, 0, vcondeq, vec_cond)
-DEF_INTERNAL_OPTAB_FN (VCOND_MASK, 0, vcond_mask, vec_cond_mask)
-
-DEF_INTERNAL_OPTAB_FN (VEC_SET, 0, vec_set, vec_set)
-DEF_INTERNAL_OPTAB_FN (VEC_EXTRACT, 0, vec_extract, vec_extract)
+DEF_INTERNAL_OPTAB_FN (VCOND, ECF_CONST | ECF_NOTHROW, vcond, vec_cond)
+DEF_INTERNAL_OPTAB_FN (VCONDU, ECF_CONST | ECF_NOTHROW, vcondu, vec_cond)
+DEF_INTERNAL_OPTAB_FN (VCONDEQ, ECF_CONST | ECF_NOTHROW, vcondeq, vec_cond)
+DEF_INTERNAL_OPTAB_FN (VCOND_MASK, ECF_CONST | ECF_NOTHROW,
+		       vcond_mask, vec_cond_mask)
+
+DEF_INTERNAL_OPTAB_FN (VEC_SET, ECF_CONST | ECF_NOTHROW, vec_set, vec_set)
+DEF_INTERNAL_OPTAB_FN (VEC_EXTRACT, ECF_CONST | ECF_NOTHROW,
+		       vec_extract, vec_extract)
 
 DEF_INTERNAL_OPTAB_FN (LEN_STORE, 0, len_store, len_store)
 DEF_INTERNAL_OPTAB_FN (MASK_LEN_STORE, 0, mask_len_store, mask_len_store)