Thanx for the lwip-1.1.1 update.
The printf formatters removed a lot of compiler warnings for me.
But there is still one to fix.
src/netif/etharp.c:480: warning: int format, long unsigned int arg (arg 3)
In this line the formatter is S16_F and the argument is sizeof()
In my enviroment (gcc for an arm cpu) size_t is the equivalent to unsigned long.
I think we need one more printf formatter SIZE_T_F or simple cast the result of sizeof().