launcher/CMake: Add symlink to bin on Linux #581
                
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So it's available in $PATH
Since CMAKE_INSTALL_BINDIR is overridden to CMAKE_INSTALL_LIBDIR on Linux, hardcode the bin directory as it's universal.
We also have to do a weird dance of a temporary .link file in the build dir to get this to work correctly for distribution packaging purposes. See https://github.com/zeek/cmake/blob/master/InstallSymlink.cmake#L24