CMake Warning \(dev\) at CMP0040-WARN-missing-target.cmake:2 \(add_custom_command\):
  Policy CMP0040 is not set: The target in the TARGET signature of
  add_custom_command\(\) must exist.  Run "cmake --help-policy CMP0040" for
  policy details.  Use the cmake_policy command to set the policy and
  suppress this warning.
+
  The target name "foobar" is unknown in this context.
Call Stack \(most recent call first\):
  CMakeLists.txt:3 \(include\)
This warning is for project developers.  Use -Wno-dev to suppress it.