Adapt MINIX-specific part of tools/installboot

This is necessary to enable correct compilation of the tools version
of installboot_nbsd(8)when cross-compiling on a system close enough
to MINIX, like NetBSD 7.0.1 for example.

Change-Id: I7a12614518293e05d64d7cc189c62651fdc64734

usr.sbin/installboot/install_master.c

@@ -3,6 +3,10 @@
  *	installboot 3.0 - Make a device bootable	Author: Kees J. Bot
  *								21 Dec 1991
  */
+#if HAVE_NBTOOL_CONFIG_H
+#include "nbtool_config.h"
+#endif
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

usr.sbin/installboot/minixfs3.c

@@ -1,3 +1,7 @@
+#if HAVE_NBTOOL_CONFIG_H
+#include "nbtool_config.h"
+#endif
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>