include rc.h properly in source files

We were attempting to include rc.h in rc-misc.h instead of the source
files where it should be included.

src/rc/_usage.c

@@ -13,6 +13,7 @@
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include "rc.h"
 #include "rc-misc.h"
 #include "_usage.h"
 #include "version.h"