title: Using exsiting target as base for a new, but related target
body: <p>Say I have a cmake script with:</p>
  <pre><code>...
  add_executable(ABC abc.cpp)
  ...
  </code></pre>
  <p>with some properties set, libraries linked etc.</p>
  <p>Now I'd like to define a derived target, say <code>ABC-extended</code> based on <code>ABC</code> in the same CMakeLists.txt file, that would have all the same properties, libraries linked etc, but with a couple of new compiler flags passed say <code>-O3</code> or whatever, without redefining all that.</p>
  <p>I.e., I'd like something like this (fictional functions used):</p>
  <pre><code>add_derived_executable(ABC2 FROM ABC)
  add_target_compile_options(ABC2 PUBLIC -O3) 
  </code></pre>