tools: fix build error with mustach

mustach relies on transitive includes to work, this introduces a
wrapping header that satisfies these

Author: mroethke

third-party/mustach.h

@@ -0,0 +1,15 @@
+/*
+ * This file is part of RTRlib.
+ *
+ * This file is subject to the terms and conditions of the MIT license.
+ * See the file LICENSE in the top level directory for more details.
+ *
+ * Website: http://rtrlib.realmv6.org/
+ */
+
+/* fix missing include in the mustach header by including it first */
+
+// clang-format off
+#include <stdio.h>
+#include "third-party/mustach/mustach.h"
+// clang-format on

tools/rtrclient.c

@@ -11,7 +11,7 @@
 
 #include "rtrlib/rtrlib.h"
 
-#include "third-party/mustach/mustach.h"
+#include "third-party/mustach.h"
 #include "third-party/tommyds/tommyarray.h"
 #include "third-party/tommyds/tommyhashlin.h"
 

tools/templates.h.cmake

@@ -7,6 +7,8 @@
  * Website: http://rtrlib.realmv6.org/
  */
 
+ #include <stddef.h>
+
 
 struct pfx_output_template {
 	const char *name;