Compatibility for b64_ntop, missing from some alternative libc.

compat.h

@@ -196,6 +196,11 @@ size_t	 	 strlcat(char *, const char *, size_t);
 int	 	 daemon(int, int);
 #endif
 
+#ifndef HAVE_B64NTOP
+/* b64_ntop.c */
+int		 b64_ntop(const char *, size_t, char *, size_t);
+#endif
+
 #ifndef HAVE_FORKPTY
 /* forkpty.c */
 #include <sys/ioctl.h>