* build-aux/xgettext.scm: New script.
* po/guix/Makevars (XGETTEXT): Set it.
(XGETTEXT_OPTIONS): Add --xgettext option to `real' xgettext.
* po/packages/Makevars (XGETTEXT): Set it.
(XGETTEXT_OPTIONS): Add --xgettext option to `real' xgettext.
Change-Id: I71b6b843970090f765f46ac346b92a346560e3f0