Conditionalize packages that RHEL/EPEL 7/8 don't provide
    
    EPEL 7 and 8 provide libsidplayfp-devel, but since at least audacious
    4.3, libsidplayfp-devel >= 2.0 is required.
    
    RHEL 8 provides pkgconfig(libpipewire-0.3) and pkgconfig(libspa-0.2),
    but audacious requires libpipewire-0.3 >= 0.3.26 and libspa-0.2 >= 0.2;
    RHEL 8 only provides pipewire-0.3.6-1.
    
    Neither RHEL nor EPEL 7 and 8 provide ffmpeg (pkgconfig(libavcodec) >=
    56.60.100, pkgconfig(libavformat) >= 56.40.101 and pkgconfig(libavutil)
    >= 54.31.100); EPEL 9 starts providing ffmpeg.