[Committed] Tweak new test case gcc.target/i386/dec-cmov-2.c

With -m32, this test case is sensitive to the instruction timings of
the target (for ifcvt to normalize bar() to foo() during the ce1 pass,
prior to the transformations actually being tested here).  Specifying
-march=core2 prevents these failures.  Committed as obvious.

2021-07-31  Roger Sayle  <roger@nextmovesoftware.com>

gcc/testsuite/ChangeLog
	* gcc.target/i386/dec-cmov-2.c: Require -march=core2 with -m32.

gcc/testsuite/gcc.target/i386/dec-cmov-2.c

@@ -1,6 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-O2" } */
-/* { dg-additional-options "-march=pentiumpro -mregparm=3" { target ia32 } } */
+/* { dg-additional-options "-march=core2 -mregparm=3" { target ia32 } } */
 
 int foo(int x)
 {