Drop go-rpm-macros for RHEL
    
    As go-rpm-macros are still not part of RHEL Buildroot, let's add the
    conditional and only use it on Fedora.
    
    This change requires:
    - explicitly setting "_find_debuginfo_dwz_opts" and
      "_dwz_low_mem_die_limit", for generating the debug packages when not
      using go-rpm-macros;
    
    - explicitly define gobuild, in case its not defined;
      - The definition was taken from Fedora 33 podman.spec and tested on
        RHEL 8.2;
    
    - depend on golang instead of go-rpm-macros when building on RHEL;
    
    - depend on compiler(go-compiler), in order to have debugsource and
      debuginfo packages generated, when building on RHEL.
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>