cmake file(VERBOSE) examples

opencv/opencv cmake/OpenCVPCHSupport.cmake :301

    file(GENERATE OUTPUT "${_pch_generate_file_cmd}" CONTENT "#!/bin/sh
if [ -n \"$VERBOSE\" ]; then
  tail -n1 \$0
fi
${_command} '-D$<JOIN:$<TARGET_PROPERTY:${_targetName},COMPILE_DEFINITIONS>,' '-D>'
")