title: CMake. Cann't get target output file name
body: <p>I use CMake 3.10. Previously I've used 3.5.
  According manual i can use $ to get some path to output file. In fact anything isn't printed.</p>
  
  <p>Status is "-- lib_location == $" I looked into examples of </p>
  
  <p>But if I use next construction, it works well.</p>
  
  <pre><code>add_custom_target(
    testTartgetFile ALL
    COMMAND ${CMAKE_COMMAND} -E echo "$&lt;TARGET_FILE:tgt1&gt;"
    VERBATIM
  )
  </code></pre>
  
  <p>The question is how to get target object? I need it for further handling, not for print out.</p>
  
  <p>My code:</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.0)
  
  project(libtest_project)
  
  function(add_txbundle)
      set(options NONE)
      set(oneValueArgs TARGET)
      set(multiValueArgs EXTRA_MAPPINGS  DEPENDENCIES)
      set(txPrefix "TxBundle")
      cmake_parse_arguments(${txPrefix} "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
  
      message(status " TARGET ${${txPrefix}_TARGET}")
      message(status " EXTRA_MAPPINS ${TxBundle_EXTRA_MAPPINGS}")
  
      set(TxBundleTarget "${${txPrefix}_TARGET}.txbundle")
      set(TxParentTarget "${${txPrefix}_TARGET}")
  
      message(status " TX TARGET ${TxBundleTarget}")
      #..... some actions ...
  
  endfunction(add_txbundle)
  
  add_library(testlb SHARED testlib.cpp)
  message (STATUS "lib_location == $&lt;TARGET_FILE:testlb&gt;")    
  add_txbundle(TARGET testlb EXTRA_MAPPINGS "1:1")
  </code></pre>