Vendor dependencies

Let's see how I like this workflow.

vendor/pin-project-lite/tests/compiletest.rs

@@ -0,0 +1,15 @@
+#![cfg(not(miri))]
+#![warn(rust_2018_idioms, single_use_lifetimes)]
+
+use std::env;
+
+#[rustversion::attr(not(nightly), ignore)]
+#[test]
+fn ui() {
+    if env::var_os("CI").is_none() {
+        env::set_var("TRYBUILD", "overwrite");
+    }
+
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/**/*.rs");
+}