sycl

In #3978 I extended the test a bit by adding more explicit template instantiations to get bigger coverage in the test, which actually allowed to find one more warning.

Besides increased coverage, I've also discovered that some warnings are disabled for no (or at least unknown to me) reason and could be enabled back to improve our headers and tests further: intel/llvm#397

Just an FYI whilst I was trawling through the ROCm GitHub page:

https://rocmdocs.amd.com/en/latest/Programming_Guides/Programming-Guides.html#

The problem is that the OpenCL types in https://github.com/triSYCL/triSYCL/blob/master/include/triSYCL/opencl_types.hpp are defined on the host according to the x86-64 Linux ABI which depends on the CPU & OS instead of using the description from https://www.khronos.org/registry/OpenCL/specs/2.2/html/OpenCL_C.html#built-in-scalar-data-types

Note that the system-wide cl_size_t has been removed

The cl_ types are not needed in general, however they should still be kept in the OpenCL C interop sample code.

Things like XILINX_XRT which are set by the user and others like XILINX_DEVICE_ONLY that are set by the compiler but affect the code users compile may be useful to add.