According to the gettext manual, AM_GNU_GETTEXT_VERSION sets the
minimum gettext version required to build the package but it doesn't
look quite right as my system insist on using that exact version of
gettext to install the po files.
AC_C_CONST
AC_STRUCT_TM
-# It looks like gettext 0.15.1 does contain all the features we need
-# but autopoint 0.17 cannot parse 0.15.1 so it is rounded up.
-AM_GNU_GETTEXT_VERSION([0.16])
+# Change the gettext version according to the available version on your system.
+# It should not be necessary to change it unless you run autoreconf -fi.
+AM_GNU_GETTEXT_VERSION([0.18])
AM_GNU_GETTEXT([external])
AC_SYS_LARGEFILE