This command does not support generator expressions. The documentation was mistakenly extended to claim it in commit v3.0.0-rc1~60^2~3 (Help: Mark up the buildsystem commands documentation, 2014-02-03).
Cross-link to the cmake-buildsystem manual.
Run the convert-help.bash script to convert documentation: ./convert-help.bash "/path/to/CMake-build/bin" Then remove it.