po, examples: Use case-insensitive search for "GNU <PACKAGE_NAME>".
Reported by Akim Demaille <akim@lrde.epita.fr> in
<https://lists.gnu.org/archive/html/bug-gettext/2018-10/msg00020.html>.
* gettext-runtime/po/Makefile.in.in ($(DOMAIN).pot-update): Use a
case-insensitive search for "GNU <PACKAGE_NAME>".
* gettext-tools/examples/hello-*/po/Makefile.am ($(DOMAIN).pot-update):
Likewise.
* gettext-tools/examples/hello-objc-gnustep/po/GNUmakefile
($(DOMAIN).pot-update): Likewise.
