title: From CMake setup 'make' to use '-j' option by default
body: <p>I want my CMake project to be built by <code>make -j N</code>, whenever I call <code>make</code> from the terminal. I don't want to set <code>-j</code> option manually every time.</p>
  
  <p>For that, I set <em>CMAKE_MAKE_PROGRAM</em> variable to the specific command line. I use the <code>ProcessorCount()</code> function, which gives the number of procesors to perform build in parallel.</p>
  
  <p>When I do <code>make</code>, I do not see any speed up. However if I do <code>make -j N</code>, then it is built definitely faster.</p>
  
  <p>Would you please help me on this issue? (I am developing this on Linux.)</p>
  
  <p>Here is the snippet of the code that I use in <code>CMakeList.txt</code>:</p>
  
  <pre><code>include(ProcessorCount)
  ProcessorCount(N)
  message("number of processors: "  ${N})
  if(NOT N EQUAL 0)
    set(CTEST_BUILD_FLAGS -j${N})
    set(ctest_test_args ${ctest_test_args} PARALLEL_LEVEL ${N})
    set(CMAKE_MAKE_PROGRAM "${CMAKE_MAKE_PROGRAM} -j ${N}")      
  endif()
  message("cmake make program" ${CMAKE_MAKE_PROGRAM})
  </code></pre>
  
  <p>Thank you very much.</p>