Properly escape nested macro calls
    
    %python%{pyver}_sitelib only works when %python is not defined.
    Now it is and this fails.
    
    For reference, this is possible in Fedora and EPEL:
    
        %if ...
        %global __python %__python3
        %else
        %global __python %__python2
        %endif
    
        %python_sitelib -> /usr/lib/python3.8/site-packages
        %py_build -> /usr/bin/python3 setup.py  build ...
        %py_install -> /usr/bin/python3 setup.py  install ...
        %python -> /usr/bin/python3
    
    So the %pyver macros are not in fact needed at all. However some RDO macros might interfere here.