Vendor dependencies

Let's see how I like this workflow.

vendor/tokio/tests/signal_no_rt.rs

@@ -0,0 +1,12 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+#![cfg(unix)]
+
+use tokio::signal::unix::{signal, SignalKind};
+
+#[cfg_attr(tokio_wasi, ignore = "Wasi does not support panic recovery")]
+#[test]
+#[should_panic]
+fn no_runtime_panics_creating_signals() {
+    let _ = signal(SignalKind::hangup());
+}