Inter-Kernel and Kernel-Host Pipes in one design

This issue was successfully reproduced.

You can use the sycl::ext::intel::experimental::pipe as an inter-kernel pipe or as a host pipe. I was able to get your code to compile by changing ProducerToConsumerPipe as so:

using ProducerToConsumerPipe = ext::intel::experimental::pipe< // Defined in the SYCL headers.
    class ProducerConsumerPipeId,                // An identifier for the pipe.
    INTRA_KERNEL_TYPE,                           // The type of data in the pipe.
    4>;                                          // The capacity of the pipe.

It's odd that you can't have a mixture of experimental pipes and non-experimental pipes; we've opened a bug report internally on this. Thanks for reporting!