title: How to override optimization level flag in modern CMake
body: <p>What's the recommended way of overriding optimization level flags (<code>-O2</code>, <code>-O3</code> etc. and the MSVC-counterparts with <code>/</code>)?</p>
  
  <p><code>target_compile_options(mytarget PUBLIC "$&lt;$&lt;CONFIG:RELWITHDEBINFO&gt;:/Od&gt;")</code></p>
  
  <p>This results in the compiler output:</p>
  
  <blockquote>
    <p>cl : Command line warning D9025 : overriding '/O2' with '/Od'</p>
  </blockquote>
  
  <p>I am happy to use the latest CMake, 3.13.2.</p>