CC: gettext-full: make autopoint and gettextize reloctable

The autopoint and gettextize host utilities contain hardcoded staging dir
paths which need to be overridden for the SDK environment.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

Backport of r48208

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@48211 3c298f89-4303-0410-b956-a3cf2f4a3e73