[clang] [SYCL] Basic code generation for SYCL kernel caller offload entry point functions. (PR #133030)

[Erich Keane via cfe-commits]

erichkeane wrote:

I can't find our conversation again and firefox crashed before I could submit, but PLEASE make sure the mangling tests cover the examples we put together.  

ALSO, we don't always mangle the types of lambdas, we sometimes do $_0 and $_1 (source of another bug) for ones without external linkage.

https://github.com/llvm/llvm-project/pull/133030