Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tests/ui/deny_elided_lifetimes.rs

@@ -0,0 +1,27 @@
+#![deny(elided_lifetimes_in_paths)]
+
+#[cxx::bridge]
+mod ffi {
+    #[derive(PartialEq, PartialOrd, Hash)]
+    struct Struct<'a> {
+        reference: &'a i32,
+    }
+
+    extern "Rust" {
+        type Rust<'a>;
+    }
+
+    unsafe extern "C++" {
+        type Cpp<'a>;
+
+        fn lifetime_named<'a>(s: &'a i32) -> UniquePtr<Cpp<'a>>;
+
+        fn lifetime_underscore(s: &i32) -> UniquePtr<Cpp<'_>>;
+
+        fn lifetime_elided(s: &i32) -> UniquePtr<Cpp>;
+    }
+}
+
+pub struct Rust<'a>(&'a i32);
+
+fn main() {}