don't double-apply variant padding to const enums

Fixes #38002.

src/test/run-pass/issue-38002.rs

@@ -0,0 +1,45 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that constant ADTs are translated OK, part k of N.
+
+#![feature(slice_patterns)]
+
+enum Bar {
+    C
+}
+
+enum Foo {
+    A {},
+    B {
+        y: usize,
+        z: Bar
+    },
+}
+
+const LIST: [(usize, Foo); 2] = [
+    (51, Foo::B { y: 42, z: Bar::C }),
+    (52, Foo::B { y: 45, z: Bar::C }),
+];
+
+pub fn main() {
+    match LIST {
+        [
+            (51, Foo::B { y: 42, z: Bar::C }),
+            (52, Foo::B { y: 45, z: Bar::C })
+        ] => {}
+        _ => {
+            // I would want to print the enum here, but if
+            // the discriminant is garbage this causes an
+            // `unreachable` and silent process exit.
+            panic!("trivial match failed")
+        }
+    }
+}