title: How can I configure cmake to compile a file twice with two different compilers?
body: <p>I'm adding a SYCL/OpenCL kernel to a parallel C++ program which is built with cmake.  Using SYCL means I need to get cmake to compile my C++ source file twice: once with the SYCL compiler, and once with the project's default compiler, which is GCC.  Both compilations produce outputs which need to be included when linking.  </p>
  
  <p>I'm completely new to cmake.  I've added the GCC compile and link steps to the project's CMakeLists.txt, but what's the best way to add the SYCL compile step?  I'm currently trying the "add_custom_command" option with "PRE_BUILD", but the command which is run doesn't seem to know about the paths which are provided to the normal compile and link steps: the current working directory, include directories, source directories, etc.  I'm having to specify all of these manually, and I'm having to figure some of them out first.</p>
  
  <p>It feels like I'm doing this the hard way.  Is there a recommended (or at least better) way to get cmake to compile a file twice with two different compilers?</p>
  
  <p>Also, there used to be a SYCL tag, but it's disappeared.  Can someone recreate it, please?</p>