Since we are force enabling the mandatory tail calls on Windows x64,
even at the expense of stack traces and debugging support, adjust the
tests to account for the difference.
If target doesn't support musttail (e.g. WebAssembly), the function
passed to coro.end.async can return control back to the caller.
So the frontend should emit 'ret void' instead of unreachable after the
coro.end.async intrinsic call to allow such situation.
