Merge from rustc

Author: RalfJung

src/eval.rs

@@ -363,7 +363,7 @@ pub fn create_ecx<'mir, 'tcx: 'mir>(
                 tcx,
                 ty::ParamEnv::reveal_all(),
                 start_id,
-                tcx.mk_substs(::std::iter::once(ty::subst::GenericArg::from(main_ret_ty))),
+                tcx.intern_substs(&[ty::subst::GenericArg::from(main_ret_ty)]),
             )
             .unwrap()
             .unwrap();

src/machine.rs

@@ -907,8 +907,9 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
                 panic!("extern_statics cannot contain wildcards")
             };
             let (shim_size, shim_align, _kind) = ecx.get_alloc_info(alloc_id);
+            let def_ty = ecx.tcx.type_of(def_id).subst_identity();
             let extern_decl_layout =
-                ecx.tcx.layout_of(ty::ParamEnv::empty().and(ecx.tcx.type_of(def_id))).unwrap();
+                ecx.tcx.layout_of(ty::ParamEnv::empty().and(def_ty)).unwrap();
             if extern_decl_layout.size != shim_size || extern_decl_layout.align.abi != shim_align {
                 throw_unsup_format!(
                     "`extern` static `{name}` from crate `{krate}` has been declared \