Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tests/ui/enum_match_without_wildcard.stderr

@@ -0,0 +1,17 @@
+error[E0004]: non-exhaustive patterns: `ffi::A { repr: 2_u8..=u8::MAX }` not covered
+  --> tests/ui/enum_match_without_wildcard.rs:12:11
+   |
+12 |     match a {
+   |           ^ pattern `ffi::A { repr: 2_u8..=u8::MAX }` not covered
+   |
+note: `ffi::A` defined here
+  --> tests/ui/enum_match_without_wildcard.rs:3:10
+   |
+3  |     enum A {
+   |          ^
+   = note: the matched value is of type `ffi::A`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+14 ~         ffi::A::FieldB => 2021,
+15 ~         ffi::A { repr: 2_u8..=u8::MAX } => todo!(),
+   |