Add option to use built-in run-parts instead of /bin/run-parts

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>

helpers.h

@@ -4,6 +4,9 @@
 int	makepath	(char *);
 void	ifconfig	(char *, char *, char *, int);
 void	copyfile	(char *, char *, int);
+
+#ifdef BUILTIN_RUNPARTS
 int	run_parts	(char *, ...);
+#endif
 
 #endif