Revert "Encode const constructor MIR in crate metadata"

This reverts commit 2010e0a.

For now, we'll let this ICE and deal with it later since it's
feature-gated anyway. Also add known-bug test for it.

compiler/rustc_mir_transform/src/lib.rs

@@ -21,7 +21,7 @@ use rustc_const_eval::util;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_data_structures::steal::Steal;
 use rustc_hir as hir;
-use rustc_hir::def::DefKind;
+use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::IndexVec;
 use rustc_middle::mir::{
@@ -322,7 +322,7 @@ fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
     for item in tcx.hir_crate_items(()).free_items() {
         if let DefKind::Struct | DefKind::Enum = tcx.def_kind(item.owner_id) {
             for variant in tcx.adt_def(item.owner_id).variants() {
-                if let Some((_, ctor_def_id)) = variant.ctor {
+                if let Some((CtorKind::Fn, ctor_def_id)) = variant.ctor {
                     set.insert(ctor_def_id.expect_local());
                 }
             }

tests/crashes/132985.rs

@@ -0,0 +1,17 @@
+//@ known-bug: #132985
+//@ aux-build:aux132985.rs
+
+#![allow(incomplete_features)]
+#![feature(min_generic_const_args)]
+#![feature(adt_const_params)]
+
+extern crate aux132985;
+use aux132985::Foo;
+
+fn bar<const N: Foo>() {}
+
+fn baz() {
+    bar::<{ Foo }>();
+}
+
+fn main() {}

tests/crashes/auxiliary/aux132985.rs

@@ -0,0 +1,6 @@
+#![feature(adt_const_params)]
+
+use std::marker::ConstParamTy;
+
+#[derive(Eq, PartialEq, ConstParamTy)]
+pub struct Foo;