(CMake Error at BadCommand.cmake:1 \(add_custom_command\):
  Error evaluating generator expression:

    \$<OUTPUT_CONFIG:a>

  Expression did not evaluate to a known generator expression
Call Stack \(most recent call first\):
  CMakeLists.txt:3 \(include\)


)+(CMake Error at BadCommand.cmake:2 \(add_custom_command\):
  Error evaluating generator expression:

    \$<COMMAND_CONFIG:b>

  Expression did not evaluate to a known generator expression
Call Stack \(most recent call first\):
  CMakeLists.txt:3 \(include\)


)+