Add dependent system includes to make sudo_*.h more standalone.

In the past we've relied on the various .c files to include the
system headers that define types that the sudo_*.h headers require.
This is fragile and can cause issues when includes get re-ordered.

include/sudo_debug.h

@@ -19,13 +19,13 @@
 #ifndef SUDO_DEBUG_H
 #define SUDO_DEBUG_H
 
+#include <sys/types.h>		/* for id_t, size_t, ssize_t, time_t */
 #include <stdarg.h>
 #ifdef HAVE_STDBOOL_H
 # include <stdbool.h>
 #else
 # include "compat/stdbool.h"
 #endif
-#include <sys/types.h>
 #include "sudo_queue.h"
 
 /*