cmake HAVE_CYGWIN examples

JulNadeauCA/libagar CMakeChecks.cmake :527

check_c_source_compiles("
#include <sys/types.h>
#include <sys/stat.h>
#include <windows.h>

int main(int argc, char *argv[]) {
	struct stat sb;
	DWORD rv;
	rv = GetFileAttributes(\"foo\");
	stat(\"foo\", &sb);
	return(0);
}
" HAVE_CYGWIN)