Fix objcImplementattion and non-Darwin builds

Author: drexin

lib/IRGen/GenMeta.cpp

@@ -3638,6 +3638,9 @@ namespace {
     }
 
     void addLayoutStringPointer() {
+      if (asImpl().getFieldLayout().hasObjCImplementation())
+        return;
+
       if (auto *layoutString = getLayoutString()) {
         B.add(layoutString);
       } else {

stdlib/public/runtime/ErrorObjectNative.cpp

@@ -60,7 +60,7 @@ static SWIFT_CC(swift) void _destroyErrorObject(SWIFT_CONTEXT HeapObject *obj) {
 
 /// Heap metadata for Error boxes.
 static const FullMetadata<HeapMetadata> ErrorMetadata{
-  HeapMetadataHeader{{_destroyErrorObject}, {&VALUE_WITNESS_SYM(Bo)}},
+  HeapMetadataHeader{{nullptr}, {_destroyErrorObject}, {&VALUE_WITNESS_SYM(Bo)}},
   HeapMetadata(MetadataKind::ErrorObject),
 };