Add out-of-source builds controlled by a macro
    
    This will allow us to port packages to the %cmake_build/%cmake_install
    even on older Fedora with possibility to easily opt-in for out-of-source
    builds by `%global __cmake_out_of_source_build 1`. In future we will
    make it opt-out (`%global __cmake_out_of_source_build 0` will do
    in-source builds again).
    
    Signed-off-by: Igor Raits <ignatenkobrain@fedoraproject.org>