Just in case you are wondering... rpm SPEC file comments do absolutely nothing... at all.
%install #%makeinstall make install DESTDIR=$RPM_BUILD_ROOT
CMake Error at cmake_install.cmake:41 (FILE): file INSTALL cannot copy file "/home/stou/rpmbuild/BUILD/generatorrunner-0.3.3/build/libgenrunner.so.0.3.3" to "/usr/lib64/libgenrunner.so.0.3.3".
How do you like that? Did you just waste 2 hours of your life? Well maybe you shouldn't expect things to work as documented. Best of all... someone knew about this but failed to mention it (but I am not bitter).