Fix pr81923 test for targets using __USER_LABEL_PREFIX__

2018-08-16  Iain Sandoe <iain@sandoe.co.uk>

gcc/testsuite

	* gcc.dg/asan/pr81923.c: Stringify __USER_LABEL_PREFIX__.

From-SVN: r263577

gcc/testsuite/ChangeLog

+2018-08-16  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* gcc.dg/asan/pr81923.c: Stringify __USER_LABEL_PREFIX__.
+
 2018-08-15  Uros Bizjak  <ubizjak@gmail.com>
 
 	* gcc.target/i386/rop1.c: Remove.

gcc/testsuite/gcc.dg/asan/pr81923.c

 /* PR sanitizer/81923 */
 /* { dg-do link } */
 
-int foobar __asm (__USER_LABEL_PREFIX__ "barbaz") = 34;
+#define STR1(X) #X
+#define STR2(X) STR1(X)
+
+int foobar __asm (STR2(__USER_LABEL_PREFIX__) "barbaz") = 34;
 
 int
 main ()