Allow evaluating trivial drop glue in constants

src/test/ui/consts/drop_none.rs

@@ -0,0 +1,13 @@
+// compile-pass
+#![allow(dead_code)]
+struct A;
+impl Drop for A {
+    fn drop(&mut self) {}
+}
+
+const FOO: Option<A> = None;
+
+const BAR: () = (FOO, ()).1;
+
+
+fn main() {}