gcc.dg/torture/pr113255.c: Fix ia32 test failure

Fix ia32 test failure:

FAIL: gcc.dg/torture/pr113255.c   -O1  (test for excess errors)
Excess errors:
cc1: error: '-mstringop-strategy=rep_8byte' not supported for 32-bit code

	PR rtl-optimization/113255
	* gcc.dg/torture/pr113255.c (dg-additional-options): Add only
	if not ia32.