Vendor dependencies

Let's see how I like this workflow.

vendor/bitflags/tests/compile-pass/impls/convert.rs

@@ -0,0 +1,17 @@
+use bitflags::bitflags;
+
+bitflags! {
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+impl From<u32> for Flags {
+    fn from(v: u32) -> Flags {
+        Flags::from_bits_truncate(v)
+    }
+}
+
+fn main() {
+
+}