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

[Tom Honermann via llvm-commits]

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tahonermann wrote:

Previous discussion regarding where to locale offload related libraries can be found [here](https://discourse.llvm.org/t/rfc-llvm-policy-for-top-level-directories-and-language-runtimes/86143). I don't think a consensus has been reached there. I prefer the top-level directory location for a few reasons: 1) libsycl won't have a dependency on offload until the latter has matured to the point that the UnifiedRuntime library is no longer needed, 2) libsycl could conceivably retain a build mode that doesn't depend on either offload or the UnifiedRuntime library; e.g., for a configuration that schedules kernels on a CPU thread pool, and 3) I don't agree with the arguments for placing everything related to offload under the offload directory.

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