Gate const drop behind const_destruct feature, and fix const_precise_…

…live_drops post-drop-elaboration check

core/src/marker.rs

@@ -953,7 +953,7 @@ marker_impls! {
 ///
 /// This should be used for `~const` bounds,
 /// as non-const bounds will always hold for every type.
-#[unstable(feature = "const_trait_impl", issue = "67792")]
+#[unstable(feature = "const_destruct", issue = "10")]
 #[lang = "destruct"]
 #[rustc_on_unimplemented(message = "can't drop `{Self}`", append_const_msg)]
 #[rustc_deny_explicit_impl(implement_via_object = false)]