Add support for new C++ preprocessing number tokens.
Reported by Moritz Bunkus <moritz@bunkus.org>
at <https://savannah.gnu.org/bugs/?50117>.
* gettext-tools/src/x-c.c (phase5_get): Recognize C++14 and C++17 extensions of
preprocessing number tokens.
* gettext-tools/tests/xgettext-c-22: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add it.
* NEWS: Mention the change.
