Improve PR64242 testcase

Clear the input array to avoid the testcase accidentally
passing with an incorrect frame pointer.

Committed as obvious.

testsuite/
	PR middle-end/64242
	* gcc.c-torture/execute/pr64242.c: Improve test.

From-SVN: r272382

gcc/testsuite/ChangeLog

+2019-06-17  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	PR middle-end/64242
+	* gcc.c-torture/execute/pr64242.c: Improve test.
+
 2019-06-16  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
 
 	* gcc.target/msp430/mspabi_sllll.c: New test.

gcc/testsuite/gcc.c-torture/execute/pr64242.c

@@ -7,6 +7,7 @@ broken_longjmp (void *p)
 {
   void *buf[32];
   __builtin_memcpy (buf, p, 5 * sizeof (void*));
+  __builtin_memset (p, 0, 5 * sizeof (void*));
   /* Corrupts stack pointer...  */
   __builtin_longjmp (buf, 1);
 }