VS_WINRT_COMPONENT
------------------

Mark a target as a Windows Runtime component for the Visual Studio generator.
Compile the target with ``C++/CX`` language extensions for Windows Runtime.
For ``SHARED`` and ``MODULE`` libraries, this also defines the
``_WINRT_DLL`` preprocessor macro.

.. note::
  Currently this is implemented only by Visual Studio generators.
  Support may be added to other generators in the future.
