Require ngettext in test of system gettext implementation
gcc currently uses ngettext in a number of places (gcc/cp/pt.c,
gcc/diagnostic.c, gcc/collect2.c). Apparently there are (or used to
be) gettext implementations that lack ngettext. See config/gettext.m4.
This patch arranges for intl/ to be compiled when the system gettext
lacks ngettext.
* configure.ac: Invoke AM_GNU_GETTEXT with need_ngettext.
* configure: Regenerate.