message: Use SystemV abi for extern "sysv64" even on Windows
diff: @@ -91,7 +91,8 @@ fn clif_sig_from_fn_sig<'tcx>(
  };
  let (call_conv, inputs, output): (CallConv, Vec<Ty<'tcx>>, Ty<'tcx>) = match abi {
  Abi::Rust => (CallConv::triple_default(triple), sig.inputs().to_vec(), sig.output()),
  - Abi::C | Abi::Unadjusted | Abi::SysV64 => (CallConv::triple_default(triple), sig.inputs().to_vec(), sig.output()),
  + Abi::C | Abi::Unadjusted => (CallConv::triple_default(triple), sig.inputs().to_vec(), sig.output()),
  + Abi::SysV64 => (CallConv::SystemV, sig.inputs().to_vec(), sig.output()),
  Abi::RustCall => {
  assert_eq!(sig.inputs().len(), 2);
  let extra_args = match sig.inputs().last().unwrap().kind {
  