gcc/testsuite/gcc.dg/cpp/mi3.h - gcc - Git at Google

 /* Another test case for over-eager multiple include optimization. */

 #ifndef GUARD
 #define GUARD
 #elif 1				/* #elif kills optimisation  */
 int c;
 #endif
	/* Another test case for over-eager multiple include optimization. */

	#ifndef GUARD
	#define GUARD
	#elif 1 /* #elif kills optimisation */
	int c;
	#endif