gcc/testsuite/gcc.dg/cpp/mi1x.h - gcc - Git at Google

 /* This header is never to have its contents visible, but it should
    still receive the optimization.  */

 #ifndef MIX_H
 #define MIX_H

 #define main wibble

 #endif
	/* This header is never to have its contents visible, but it should
	still receive the optimization. */

	#ifndef MIX_H
	#define MIX_H

	#define main wibble

	#endif