Add regression test for issue #113941 - naive layout isn't refined

tests/ui/layout/issue-113941.rs

@@ -0,0 +1,13 @@
+// build-pass
+// revisions: normal randomize-layout
+// [randomize-layout]compile-flags: -Zrandomize-layout
+
+enum Void {}
+
+pub struct Struct([*const (); 0], Void);
+
+pub enum Enum {
+    Variant(Struct),
+}
+
+fn main() {}