Looking at https://github.com/RIOT-OS/RIOT/blob/master/sys/net/include/inet_ntop.h#L30:

/*
* WARNING: Don't even consider trying to compile this on a system where
* sizeof(int) < 4.  sizeof(int) > 4 is fine; all the world's not a VAX.
*/

I wondered if this could be a problem on MSP430 and ATMega.

I've added data type size comparison to the MCU familiy pages in the wiki (see https://github.com/RIOT-OS/RIOT/wiki/Family%3A-ATmega#data-type-sizes, https://github.com/RIOT-OS/RIOT/wiki/Family%3A-MSP430#data-type-sizes, https://github.com/RIOT-OS/RIOT/wiki/Family%3A-ARM#data-type-sizes, and https://github.com/RIOT-OS/RIOT/wiki/Family:-native#data-type-sizes).