Compilation issues with oneAPI Base Toolkit 2023.0.0

[rafbiels]

As reported by @irudkin in #23 users compiling the project with oneAPI Base Toolkit 2023.0.0 and the corresponding SYCL CUDA backend plugin may run into some release-specific compilation issues. Namely:

• dpcpp executable is deprecated and replaced with icpx -fsycl
• compilation errors and/or warnings described in https://developer.codeplay.com/products/oneapi/nvidia/2023.0.0/guides/troubleshooting

A suggested solution:

1. Replace dpcpp check in src_sycl/CMakeLists.txt with an icpx check
2. Link the troubleshooting guide in the README

[DuncanMcBain]

The first part of this issue has been dealt with in #22 but the second hasn't been addressed