The llvm.coro.suspend.async intrinsic takes a function pointer as its
argument that describes how-to restore the current continuation's
context from the context argument of the continuation function. Before
we assumed that the current context can be restored by loading from the
context arguments first pointer field (first_arg->caller_context).
This allows for defining suspension points that reuse the current
context for example.
llvm.coro.id.async lowering: Add llvm.coro.preprare.async intrinsic
Blocks inlining until after the async coroutine was split.