title: Does set_target_properties in CMake override CMAKE_CXX_FLAGS?
body: <p>At the beginning of my CMake project, I'm setting general compilation flags in the variable CMAKE_CXX_FLAGS, like</p>
  
  <pre><code>set(CMAKE_CXX_FLAGS "-W -Wall ${CMAKE_CXX_FLAGS}")
  </code></pre>
  
  <p>Later on, I need to append additional configuration-specific compilation flags (stored in BUILD_FLAGS). Can I use the following command for this:</p>
  
  <pre><code>set_target_properties(${TARGET} PROPERTIES COMPILE_FLAGS ${BUILD_FLAGS})
  </code></pre>
  
  <p>or do I have to add the CMAKE_CXX_FLAGS manually:</p>
  
  <pre><code>set_target_properties(${TARGET} PROPERTIES COMPILE_FLAGS "${CMAKE_CXX_FLAGS} ${BUILD_FLAGS}")
  </code></pre>
  
  <p>to prevent CMAKE_CXX_FLAGS being overriden by BUILD_FLAGS?</p>