- Drop gcc-c++ and cmake BuildRequires, not needed.
- Add generic c_compiler BuildRequires.
- Minor cleanup of spec-file.

NOTE:
I've ignored these rpmlintwarnings already present

[ 51s] pipewire-media-session.x86_64: E: zero-length /usr/share/pipewire/media-session.d/with-alsa
[ 51s] pipewire-media-session.x86_64: W: files-duplicate /usr/share/pipewire/media-session.d/with-pulseaudio /usr/share/pipewire/media-session.d/with-jack
[ 51s] pipewire-media-session.x86_64: W: empty-%postun
[ 51s] 3 packages and 0 specfiles checked; 1 errors, 2 warnings, 1 badness; has taken 0.3 s

Should we drop either preun or postun ?
Should we ghost with-/alsa/jack/pulseaudio ?

In any case, the current changes done here should be fine/correct.