[CMake] Setting up standard library output directory

[Enno Fennema]

I am totally new to cmake and struggling.

cmake-gui tells me at the end of a Configure
that libraries will be installed to /usr/local/lib rather than
/usr/local/lib64 where theu should go.

I have added using cmake-gui first try
    CMAKE_OUTPUT_LIBRARY_DIRECTORY=/usr/local/lib64
and next try
    LIBRARY_OUTPUT_DIRECTORY=/usr/local/lib64
but cmake-gui keeps telling me
    --   libraries will be installed at: /usr/local/lib

What do I change where and how to get the desired behaviour?

Thanks for any help.
Enno