title: Cmake: use add_custom_command to copy binary to specific location failed when location doesn't exist
body: <p>I'm trying to copy all the binaries generated by cmake to a specific directory. I don't want to use EXECUTABLE_OUTPUT_PATH, keeping them in the building tree make development easier.</p>
  
  <p>So I use add_custom_command to add a post build copy</p>
  
  <pre><code># set the final binary dir
  set(PROJECT_BINARY_DIR ${PROJECT_SOURCE_DIR}/bin)
  
  # get name and location of binary, namecan change with os (cf. ".exe" suffix on windows)
  GET_TARGET_PROPERTY(EXAMPLE_BIN_NAME example LOCATION)
  # copy bin to binary folder
  ADD_CUSTOM_COMMAND(TARGET example
            POST_BUILD
            COMMAND ${CMAKE_COMMAND} -E copy ${EXAMPLE_BIN_NAME} ${PROJECT_BINARY_DIR}/.
  )
  </code></pre>
  
  <p>The problem is that at the first build the "bin" folder doesn't exist (the copy fail), but the "bin" folder is created just after. So at the second build the copy works.</p>
  
  <p>Is there a way to make the custom command create the bin folder and then copy the binary ?
  Or is it possible to have two EXECUTABLE_OUTPUT_PATH with cmake ?</p>
  
  <p>Thanks !</p>