intltool: host variant needs host-gettext

Fixes issues like:
http://autobuild.buildroot.net/results/1c7d2e50b622179aff469fddedaa4dc2015fb496/
http://autobuild.buildroot.net/results/7d85ff51b339f1da720bb079eb05e7fba179f101/


and probably a lot more.

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