rusticl: basic DPCPP/SyCL support
This MR adds a few workarounds so that SyCL applications compiled with DPCPP can practically run on top of rusticl. It still needs RUSTICL_DEBUG=allow_invalid_spirv
to be set as there are still a couple of SPIR-V spec violations going on.
But those hacks aren't terrible and hopefully in the future we won't need them.