CMake Warning \(policy\) in CMakeLists\.txt:
  Policy CMP0081 is not set: Relative paths not allowed in LINK_DIRECTORIES
  target property\.  Run "cmake --help-policy CMP0081" for policy details\.
  Use the cmake_policy command to set the policy and suppress this warning\.

  Found relative path while evaluating link directories of "foo":

    "\.\./lib"

This warning is for project developers\.  Use -Wno-author or -Wno-policy to
suppress it\.
