Fix the CMake add_executable option for samples

[ldilley]

Either use the cmake_policy option and set it to "OLD" or use the CMake 3.x method to create binaries without including an explicit forward slash in the target.

CMake Warning (dev) at CMakeLists.txt:21 (add_executable):

  Policy CMP0037 is not set: Target names should not be reserved and should

  match a validity pattern.  Run "cmake --help-policy CMP0037" for policy

  details.  Use the cmake_policy command to set the policy and suppress this

  warning.

  The target name "samples/list" is reserved or not valid for certain CMake

  features, such as generator expressions, and may result in undefined

  behavior.

This warning is for project developers.  Use -Wno-dev to suppress it.