Try adding 'BuildRequires: gcc-c++' to the specfile
checking for x86_64-redhat-linux-gcc... gcc checking whether the C compiler works... no configure: error: in `/builddir/build/BUILD/hello-2.10': configure: error: C compiler cannot create executables See `config.log' for more details
Checking for unpackaged file(s): /usr/lib/rpm/check-files /builddir/build/BUILDROOT/hello-2.10-1.fc39.x86_64 error: Installed (but unpackaged) file(s) found: /usr/share/info/hello.info.gz /usr/share/locale/bg/LC_MESSAGES/hello.mo /usr/share/locale/ca/LC_MESSAGES/hello.mo /usr/share/locale/da/LC_MESSAGES/hello.mo /usr/share/locale/de/LC_MESSAGES/hello.mo /usr/share/locale/el/LC_MESSAGES/hello.mo /usr/share/locale/eo/LC_MESSAGES/hello.mo /usr/share/locale/es/LC_MESSAGES/hello.mo /usr/share/locale/et/LC_MESSAGES/hello.mo /usr/share/locale/eu/LC_MESSAGES/hello.mo /usr/share/locale/fa/LC_MESSAGES/hello.mo /usr/share/locale/fi/LC_MESSAGES/hello.mo /usr/share/locale/fr/LC_MESSAGES/hello.mo /usr/share/locale/ga/LC_MESSAGES/hello.mo /usr/share/locale/gl/LC_MESSAGES/hello.mo /usr/share/locale/he/LC_MESSAGES/hello.mo /usr/share/locale/hr/LC_MESSAGES/hello.mo /usr/share/locale/hu/LC_MESSAGES/hello.mo /usr/share/locale/id/LC_MESSAGES/hello.mo /usr/share/locale/it/LC_MESSAGES/hello.mo /usr/share/locale/ja/LC_MESSAGES/hello.mo /usr/share/locale/ka/LC_MESSAGES/hello.mo /usr/share/locale/ko/LC_MESSAGES/hello.mo /usr/share/locale/lv/LC_MESSAGES/hello.mo /usr/share/locale/ms/LC_MESSAGES/hello.mo /usr/share/locale/nb/LC_MESSAGES/hello.mo /usr/share/locale/nl/LC_MESSAGES/hello.mo /usr/share/locale/nn/LC_MESSAGES/hello.mo /usr/share/locale/pl/LC_MESSAGES/hello.mo /usr/share/locale/pt/LC_MESSAGES/hello.mo /usr/share/locale/pt_BR/LC_MESSAGES/hello.mo /usr/share/locale/ro/LC_MESSAGES/hello.mo /usr/share/locale/ru/LC_MESSAGES/hello.mo /usr/share/locale/sk/LC_MESSAGES/hello.mo /usr/share/locale/sl/LC_MESSAGES/hello.mo /usr/share/locale/sr/LC_MESSAGES/hello.mo /usr/share/locale/sv/LC_MESSAGES/hello.mo /usr/share/locale/th/LC_MESSAGES/hello.mo /usr/share/locale/tr/LC_MESSAGES/hello.mo /usr/share/locale/uk/LC_MESSAGES/hello.mo /usr/share/locale/vi/LC_MESSAGES/hello.mo /usr/share/locale/zh_CN/LC_MESSAGES/hello.mo /usr/share/locale/zh_TW/LC_MESSAGES/hello.mo /usr/share/man/man1/hello.1.gz
Scratch that idea, looking ate the buildlog you have unpacked files, use this to install the .mo files.
https://fedoraproject.org/wiki/PackagingDrafts/find_lang
and add the man file to the %files section.
%{_mandir}/man1/hello.1.*