MDEV-12469: static_assert cannot be determined on bigendian

Signed-off-by: Daniel Black <daniel.black@au.ibm.com>

storage/rocksdb/rdb_datadic.cc

@@ -1303,7 +1303,7 @@ static int rdb_unpack_floating_point(
   // On little-endian, swap the bytes around
   swap_func(dst, tmp);
 #else
-  static_assert(swap_func == nullptr, "Assuming that no swapping is needed.");
+  DBUG_ASSERT(swap_func == nullptr);
 #endif
 
   return UNPACK_SUCCESS;