add #[repr(C)] to the union

nikomatsakis · nikomatsakis · commit 219a584dca6e · 2019-01-10T11:51:48.000-05:00
diff --git a/reference/src/layout/enums.md b/reference/src/layout/enums.md
@@ -180,6 +180,7 @@ This will be laid out equivalently to the following more
 complex Rust types:
 
 ```
+#[repr(C)]
 union TwoCasesRepr {
     A: TwoCasesVariantA,
     B: TwoCasesVariantB,
