Avoid crash on macOS 14.
Reported by Shupeng Xue <dspxue@gmail.com> at
<https://lists.gnu.org/archive/html/bug-gettext/2023-10/msg00001.html>.
Cf <https://github.com/aria2/aria2/issues/2083#issuecomment-1694662007>.
* gettext-runtime/m4/intlmacosx.m4 (gt_INTL_MACOSX): Link with the CoreServices
framework in addition to the CoreFoundation framework.
