Vendor dependencies

Let's see how I like this workflow.

vendor/signal-hook/ci-check.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+# We try to support some older versions of rustc. However, the support is
+# tiered a bit. Our dev-dependencies do *not* guarantee that old minimal
+# version. So we don't do tests on the older ones. Also, the
+# signal-hook-registry supports older rustc than we signal-hook.
+
+set -ex
+
+rm -f Cargo.lock
+cargo build --all --exclude signal-hook-async-std --exclude signal-hook-tokio
+
+if [ "$RUST_VERSION" = 1.36.0 ] ; then
+	exit
+fi
+
+if [ "$OS" = "windows-latest" ] || [ "$RUST_VERSION" = 1.40.0 ]; then
+	# The async support crates rely on the iterator module
+	# which isn't available for windows. So exclude them
+	# from the build.
+
+	# Also, some dependencies of the runtimes don't like 1.40.
+	EXCLUDE_FROM_BUILD="--exclude signal-hook-mio --exclude signal-hook-tokio --exclude signal-hook-async-std"
+else
+	EXCLUDE_FROM_BUILD=""
+fi
+
+export RUSTFLAGS="-D warnings"
+
+cargo test --all --all-features $EXCLUDE_FROM_BUILD
+cargo test --all $EXCLUDE_FROM_BUILD