Fix build error spotted by gcc-4.4

#elif with no clause is clearly wrong and continuing when we don't
know the byte order only defers the problem to a point where its much
harder to debug



git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@1767 fd59a12c-fef9-0310-b244-a6a79926bd2f

exec/crypto.c

@@ -37,8 +37,8 @@ typedef uint64_t ulong64;
 #define ENDIAN_LITTLE
 #elif _BYTE_ORDER == _BIG_ENDIAN
 #define ENDIAN_BIG
-#elif
-#warning "cannot detect byte order"
+#else
+#error "cannot detect byte order"
 #endif
 
 #if defined(COROSYNC_LINUX)