Allow for ninja files to regenerate themselves

scripts/templates/build.ninja.j2

@@ -1,3 +1,4 @@
+ninja_required_version = 1.3
 builddir = {{ buildroot }}
 srcroot = {{ srcroot }}
 
@@ -46,9 +47,24 @@ rule lib
     description = Archiving $name
     command = $ar qcs $out $in
 
+rule regen
+    generator = true
+    description = Regenrating build files
+    command = {{ generator }} ${builddir}
+
 {% for target in targets %}
 subninja {{ target }}/target.ninja
 {% endfor %}
 
+build $
+    {%- for buildfile in buildfiles %}
+    {{ buildfile }} $
+    {%- endfor %}
+    : regen | $
+    {%- for template in templates %}
+    {{ template }} $
+    {%- endfor %}
+    {{ generator }}
+
 # vim: et ts=4 sts=4 sw=4