Vendor dependencies

Let's see how I like this workflow.

vendor/signal-hook/tests/default.rs

@@ -0,0 +1,25 @@
+//! Check the hack of SIG_DFL for windows.
+//!
+//! Libc doesn't export SIG_DFL on windows. It seems to be 0 on all platforms, though, but just to
+//! make sure, we observe it is so. We try to read the previous signal on startup and it must be
+//! the default.
+
+extern crate libc;
+
+use libc::{sighandler_t, signal, SIGTERM};
+
+const SIG_DFL: sighandler_t = 0;
+
+#[test]
+fn sig_dfl() {
+    unsafe {
+        let prev = signal(SIGTERM, SIG_DFL);
+        assert_eq!(SIG_DFL, prev);
+    }
+}
+
+#[cfg(not(windows))]
+#[test]
+fn sig_dfl_static() {
+    assert_eq!(::libc::SIG_DFL, SIG_DFL);
+}