gnome-menu2 doesn't build on aarch64

Created by: ollieparanoid

Reported by rn3_pmOS in IRC:

i'm trying to build hildon for aarch64 device. gnome-menus2 fails. i get "./config.guess: unable to guess system type" tried copying latest config.guess to build root but, still the timestamp won't change https://paste.ubuntu.com/25653428/

The solution is probably using a similar prepare function like for chocolate-doom in #664.