gob2: needs MMU

m4 needs MMU, so does bison, and so does gob2 which uses bison.
Fixes build failure:
http://autobuild.buildroot.net/results/f942b4ac770f3c7b27c42214af5bcec49f687da1/build-end.log



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>