Need to rename the declarations in md5.h using cpp too.

https://bugs.gentoo.org/870841
--- a/libradius/porting.h
+++ b/libradius/porting.h
@@ -15,12 +15,12 @@
 
 #else
 
-#include "md5.h"
 #define MD5_DIGEST_LENGTH 16
 #define MD5Final    xrad_MD5Final
 #define MD5Init     xrad_MD5Init
 #define MD5Pad      xrad_MD5Pad
 #define MD5Update   xrad_MD5Update
+#include "md5.h"
 
 #endif