title: Why CMake generate Makefile without CMAKE_CXX_FLAGS?
body: <p>This is my full CMakeLists.txt file:</p>
  
  <pre><code>set(CMAKE_BUILD_TYPE Release)
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wshadow")
  
  set(PROJECT sample)
  project(${PROJECT})
  
  set(HEADERS
      Main.h
  )
  set(SOURCES 
      Main.cpp
  )
  
  # Add souce file to project for compile
  add_executable (${PROJECT} ${HEADERS} ${SOURCES})
  
  target_link_libraries( ${PROJECT} )
  </code></pre>
  
  <p>But, in Makefile i don't seek substring "-Wall" and other option from CMAKE_CXX_FLAGS.</p>
  
  <p>Why?</p>