The logic in libcpp/Makefile.in listing diagnostic functions in a call
to xgettext was missing cpp_warning_at, cpp_pedwarning_at and
cpp_error_at, so resulting in some messages not being extracted for
translation; add those functions to those for which messages are
extracted.
Tested with "make cpplib.pot".
* Makefile.in (po/$(PACKAGE).pot): Also handle cpp_warning_at,
cpp_pedwarning_at and cpp_error_at.
becc9a12a5