Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

vendor/thiserror/tests/ui/invalid-input-impl-anyway.rs

@@ -0,0 +1,11 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+#[error]
+pub struct MyError;
+
+fn main() {
+    // No error on the following line. Thiserror emits an Error impl despite the
+    // bad attribute.
+    _ = &MyError as &dyn std::error::Error;
+}