[llvm] [SYCL] Add libsycl, a SYCL RT library implementation project (PR #144372)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 commented:

> > Also, it would be great if we could get the precommit CI running ASAP. IIUC the basic configurations would be:
> > 
> > * libstdc++/GCC(?)
> > * MSVC STL/MSVC
> > * libunwind/libc++abi/libc++/Clang
> >   That should be pretty lean on the CI resources and could probably easily run in the GH-provided runners for now.
> 
> Could you please clarify - is it a blocker for the current PR? Can we add it in the following PRs?

I don't think it should be a blocker. I'd like it soon though, since it significantly increases confidence that code changes are correct.

https://github.com/llvm/llvm-project/pull/144372