Use cache to mkdir_p for HulkBinObj builder

Rsconscript

@@ -26,7 +26,7 @@ MB = 1024 * 1024
 
 class HulkBinObj < Builder
   def run(options)
-    FileUtils.mkdir_p(File.dirname(@target))
+    @cache.mkdir_p(File.dirname(@target))
     File.write(@target, <<EOF)
 .section ".rodata"
 .balign 4096