Don't do intra-pass validation on MIR shims

compiler/rustc_mir_transform/src/shim.rs

@@ -90,7 +90,11 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
     };
     debug!("make_shim({:?}) = untransformed {:?}", instance, result);
 
-    pm::run_passes(
+    // We don't validate MIR here because the shims may generate code that's
+    // only valid in a reveal-all param-env. However, since we do initial
+    // validation with the MirBuilt phase, which uses a user-facing param-env.
+    // This causes validation errors when TAITs are involved.
+    pm::run_passes_no_validate(
         tcx,
         &mut result,
         &[