Vendor dependencies

Let's see how I like this workflow.

vendor/bitflags/tests/compile-fail/visibility/private_flags.rs

@@ -0,0 +1,18 @@
+mod example {
+    use bitflags::bitflags;
+
+    bitflags! {
+        pub struct Flags1: u32 {
+            const FLAG_A = 0b00000001;
+        }
+
+        struct Flags2: u32 {
+            const FLAG_B = 0b00000010;
+        }
+    }
+}
+
+fn main() {
+    let flag1 = example::Flags1::FLAG_A;
+    let flag2 = example::Flags2::FLAG_B;
+}