libgxim: inherit gettext to fix build error in a non-gplv3 build.

| configure.ac:18: warning: AM_NLS is m4_require'd but not m4_defun'd
  | aclocal.m4:2363: IT_PROG_INTLTOOL is expanded from...
  | aclocal.m4:2545: AC_PROG_INTLTOOL is expanded from...
  | configure.ac:18: the top level
  | configure:12119: error: possibly undefined macro: AM_NLS
  |       If this token and others are legitimate, please use m4_pattern_allow.
  |       See the Autoconf documentation.

Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>