Vendor dependencies

Let's see how I like this workflow.

vendor/getrandom/tests/rdrand.rs

@@ -0,0 +1,15 @@
+// We only test the RDRAND-based RNG source on supported architectures.
+#![cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+
+// rdrand.rs expects to be part of the getrandom main crate, so we need these
+// additional imports to get rdrand.rs to compile.
+use getrandom::Error;
+#[macro_use]
+extern crate cfg_if;
+#[path = "../src/rdrand.rs"]
+mod rdrand;
+#[path = "../src/util.rs"]
+mod util;
+
+use rdrand::getrandom_inner as getrandom_impl;
+mod common;