Fix a `cast to pointer from integer of different size' warning.

usage() has been made a (non-void) function so that it can be
used in a pointer expression (see macro `next'). Widen the
implied integer return type of usage() so that we can cast to
a pointer without warnings.

usr.bin/window/main.c

@@ -55,7 +55,7 @@ static char rcsid[] =
 #include "char.h"
 #include "local.h"
 
-#define next(a) (*++*(a) ? *(a) : (*++(a) ? *(a) : (char *)usage()))
+#define next(a) (*++*(a) ? *(a) : (*++(a) ? *(a) : (char *)(uintptr_t)usage()))
 
 /*ARGSUSED*/
 main(argc, argv)