gettext

cde62682 - Avoid -Wundef warning in gettext.h.

Avoid -Wundef warning in gettext.h. * gnulib-local/lib/gettext.h: Test the value of ENABLE_NLS only if it is defined. Reported by Tim Rühsen <tim.ruehsen@gmx.de> in <https://lists.gnu.org/archive/html/bug-gnulib/2017-04/msg00022.html>.