CMake Error at NonValidTarget-CXX_COMPILER_FRONTEND_VARIANT.cmake:1 \(add_custom_command\):
  Error evaluating generator expression:

    \$<CXX_COMPILER_FRONTEND_VARIANT>

  \$<CXX_COMPILER_FRONTEND_VARIANT> may only be used with binary targets.  It
  may not be used with add_custom_command or add_custom_target.
Call Stack \(most recent call first\):
  CMakeLists.txt:3 \(include\)
