Allow more cases to match ~const Drop.

src/test/ui/rfc-2632-const-trait-impl/const-drop-bound.rs

@@ -0,0 +1,20 @@
+// check-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+#![feature(const_precise_live_drops)]
+
+const fn foo<T, E>(res: Result<T, E>) -> Option<T> where E: ~const Drop {
+    match res {
+        Ok(t) => Some(t),
+        Err(_e) => None,
+    }
+}
+
+pub struct Foo<T>(T);
+
+const fn baz<T: ~const Drop, E: ~const Drop>(res: Result<Foo<T>, Foo<E>>) -> Option<Foo<T>> {
+    foo(res)
+}
+
+fn main() {}