gt_INTL_MACOSX not defined by gettext.m4

[Gavin Smith]

gettext.m4 from gnulib uses a macro gt_INTL_MACOSX, but running
gnulib-tool --add-import doesn't cause this macro to be defined in the
produced configure script.

There is a definition in intlmacosx.m4 but this file is not pulled in.
I have a backup of this file intlmacosx.m4~ which was probably created
by gnulib-tool when I updated the gnulib files. My guess is that the
dependencies for the gettext module have changed so it is not pulling
in the definition of this macro.

Originally reported here:
http://lists.gnu.org/archive/html/bug-texinfo/2017-07/msg00026.html