C code that is syntactically correct only on Fridays

gen.c

#include <stdio.h>
#include <time.h>

static const char mon_name[12][3] = {
	"Jan", "Feb", "Mar", "Apr", "May", "Jun",
	"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

int
main(void)
{
	static char str[] = "Mmm dd yyyy";
	struct tm it = {0};
	do {
		mktime(&it);
		sprintf(str, "%.3s %2d %4d",
		        mon_name[it.tm_mon],
		        it.tm_mday,
		        1900 + it.tm_year);
		puts(str);
		FILE *f = fopen(str, "w");
		if (it.tm_wday == 5)
			fputs("#define ITS_FRIDAY 1", f);
		fclose(f);
		++it.tm_mday;
	} while (it.tm_year < 10000 - 1900);
}

main.c

#include <stdio.h>
#include __DATE__

#if !ITS_FRIDAY
:-)
#endif

int main(void)
{
	puts("Hello");
	return 0;
}