CMake Warning \(dev\) at CMP0049-WARN.cmake:3 \(add_library\):
  Policy CMP0049 is not set: Do not expand variables in target source
  entries.  Run "cmake --help-policy CMP0049" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  Legacy variable expansion in source file "\${tgt_srcs}" expanded to
  "empty.cpp" in target "tgt".  This behavior will be removed in a future
  version of CMake.
Call Stack \(most recent call first\):
  CMakeLists.txt:3 \(include\)
This warning is for project developers.  Use -Wno-dev to suppress it.