[testsuite] Fix PR94023 to guard case under vect_hw_misalign

As PR94023 shows, the expected SLP requires misaligned vector access
support.  This patch is to guard the check under the target condition
vect_hw_misalign to ensure that.

gcc/testsuite/ChangeLog

2020-03-09  Kewen Lin  <linkw@gcc.gnu.org>

    PR testsuite/94023
    * gcc.dg/vect/slp-perm-12.c: Expect loop vectorized messages only on
    vect_hw_misalign targets.

gcc/testsuite/ChangeLog

+2020-03-09  Kewen Lin  <linkw@gcc.gnu.org>
+
+	PR testsuite/94023
+	* gcc.dg/vect/slp-perm-12.c: Expect loop vectorized messages only on
+	vect_hw_misalign targets.
+
 2020-03-08  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/93581

gcc/testsuite/gcc.dg/vect/slp-perm-12.c

@@ -49,4 +49,4 @@ int main()
   return 0;
 }
 
-/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 1 "vect" { target vect_perm } } } */
+/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 1 "vect" { target { vect_perm && vect_hw_misalign } } } } */