spec: Explicitly call %meson_build in the %build section
    
    It was never needed before as the %meson_install macro would perform a
    project rebuild. However, most recent versions of meson have changed the
    %meson_install macro to use `--no-rebuild`, exposing then this issue on
    our spec file.
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>