aarch64: Disable mem-shift-canonical test on ILP32

This test fails on ILP32 since we're looking for a pattern that could
only be hit on LP64. Disabling the test on ILP32 since the problematic
mult pattern was never hit there, so there's nothing to test.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/mem-shift-canonical.c: Skip on ILP32.

gcc/testsuite/gcc.target/aarch64/mem-shift-canonical.c

@@ -3,6 +3,7 @@
 
 /* { dg-do compile } */
 /* { dg-options "-Os -ftree-vectorize -dp" } */
+/* { dg-require-effective-target lp64 } */
 
 
 struct T