error: `extern` block uses type `W` which is not FFI-safe: this union has unspecified layout
  --> $DIR/union-repr-c.rs:15:22
   |
LL |     static FOREIGN2: W;
   |                      ^
   |
note: lint level defined here
  --> $DIR/union-repr-c.rs:2:9
   |
LL | #![deny(improper_ctypes)]
   |         ^^^^^^^^^^^^^^^
   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this union
note: type defined here
  --> $DIR/union-repr-c.rs:9:1
   |
LL | / union W {
LL | |     a: u8,
LL | | }
   | |_^

error: aborting due to previous error