[clang] [Clang][SYCL] Introduce clang-sycl-linker to link SYCL offloading device code (Part 1 of many) (PR #112245)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I'd prefer we have SYCL linking run through LLD rather than the linker-wrapper tool approach, but I don't feel strongly enough to block this.
I see this as a temporary hack around not having a proper SPIR-V linker / backend in LLVM yet. It's less of a linker-wrapper tool and more of my assertions that every single target should be able to be targeted directly via `clang --target=...` which then lets the linker wrapper just do the part where it extracts GPU code from fat binaries, invokes `clang` on each to get an executable, then wraps that in the runtime's registration code.

https://github.com/llvm/llvm-project/pull/112245