Require Drop impls to have the same constness on its bounds as the bounds on the struct have

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

@@ -0,0 +1,17 @@
+// check-pass
+#![feature(const_trait_impl)]
+
+#[const_trait]
+trait Foo {
+    fn foo(&self) {}
+}
+
+struct Bar<T>(T);
+
+impl<T: ~const Foo> Bar<T> {
+    const fn foo(&self) {
+        self.0.foo()
+    }
+}
+
+fn main() {}