Testsuite: restrict test to nonpic targets

The test is currently failing on x86_64-apple-darwin.

gcc/testsuite/ChangeLog:

	PR testsuite/112297
	* gcc.target/i386/pr100936.c: Require nonpic target.

gcc/testsuite/gcc.target/i386/pr100936.c

 /* PR target/100936 */
 /* { dg-do assemble } */
 /* { dg-options "-O2" } */
+/* { dg-require-effective-target nonpic } */
 
 __seg_gs int var;