title: CMake custom build step PRE_LINK/PRE_BUILD do not work
body: <p>PRE_LINK and PRE_BUILD do not seem to work in CMake on linux ( generating MakeFiles ). The documentation says that only PRE_BUILD is not supported. But , PRE_LINK does not wrok at all.</p>
  
  <p>I was not sure if understood them wrong or if I am missing something.</p>
  
  <p>( For now,as workaround I added a fake target and POST_BUILD step on it. Then creating dependency worked. But, it has its own issues.For my setup , it creates problems when parallel make ( -j ) is done.</p>
  
  <p>Example Code : </p>
  
  <pre><code>cmake_minimum_required(VERSION 2.8.5)
  project(custom_command_test)
  
  add_custom_target(my_actual_target
      COMMAND echo " I am the actual taget "
      COMMENT "Running actual target"
      )
  add_custom_command(
      TARGET my_actual_target
      PRE_LINK
      COMMAND echo "I am prelinked to actual target"
      COMMENT " Running PRELINK action "
      )
  add_custom_command(
      TARGET my_actual_target
      PRE_BUILD
      COMMAND echo " I am prebuilt to actual target"
      COMMENT " Running PRE_BUILD action"
      )
  add_custom_command(
      TARGET my_actual_target
      POST_BUILD
      COMMAND echo " I postbuild to actual target"
      COMMENT " Running POST BUILD action "
      )
  </code></pre>
  
  <p>Output : </p>
  
  <pre><code>&gt; cmake .
  -- The C compiler identification is GNU 4.4.2
  -- The CXX compiler identification is GNU 4.4.2
  -- Check for working C compiler: XXXX/gcc/4.4.2/bin/gcc
  -- Check for working C compiler: XXXX/gcc/4.4.2/bin/gcc -- works
  -- Detecting C compiler ABI info
  -- Detecting C compiler ABI info - done
  -- Check for working CXX compiler: XXXX/gcc/4.4.2/bin/g++
  -- Check for working CXX compiler: XXXX/gcc/4.4.2/bin/g++ -- works
  -- Detecting CXX compiler ABI info
  -- Detecting CXX compiler ABI info - done
  -- Configuring done
  -- Generating done
  -- Build files have been written to: XXXX
  
   &gt; make my_actual_target
  Scanning dependencies of target my_actual_target
  [100%] Running actual target
   I am the actual taget 
   Running PRE_BUILD action
   I am prebuilt to actual target
   Running POST BUILD action 
   I postbuild to actual target
  [100%] Built target my_actual_target
  
  &gt; cmake --version
  cmake version 2.8.10.2
  </code></pre>
  
  <p>Any solution to this ? </p>