xkeyboard-config: add missing dependency on host-gettext and sanitize

xkeyboard-config needs msgfmt so we need to pull host-gettext into the
dependencies.
And remove GMSGFMT path hardcoding otherwise host-gettext msgfmt won't
work. Fixes:
http://autobuild.buildroot.net/results/ec956056aba54ab7993cf58a74a93a3b900dee95/



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