pptp.c and version.c depend on config.h

Upstream-Status: Backport

Upstream has already similar fixes. Will be available on next release.

Signed-off-by: Jesse Zhang <sen.zhang@windriver.com>

--- a/Makefile	2013-02-27 17:09:24.431226665 +0800
+++ b/Makefile	2013-02-27 17:09:03.442075550 +0800
@@ -43,6 +43,8 @@
 pptpsetup.8: pptpsetup
 	pod2man $? > $@
 
+pptp.o version.o: config.h
+
 config.h: 
 	echo "/* text added by Makefile target config.h */" > config.h
 	echo "#define PPTP_LINUX_VERSION \"$(VERSION)$(RELEASE)\"" >> config.h