Merge pull request #1732 from cho45/depend-build-config

Always include build_config.rb to compile dependency.

tasks/mruby_build_commands.rake

@@ -110,7 +110,7 @@ module MRuby
         File.read(file).gsub("\\\n ", "").scan(/^\S+:\s+(.+)$/).flatten.map {|s| s.split(' ') }.flatten
       else
         []
-      end
+      end + [ MRUBY_CONFIG ]
     end
   end