Fix layering violation I introduced by putting _EmptyBoxStorage into the stubs library (#10373)

* Fix layering violation I introduced by putting _EmptyBoxStorage into the stubs library

Should fix the linkage issue on linux

Author: aschwaighofer

stdlib/public/SwiftShims/GlobalObjects.h

@@ -88,13 +88,6 @@ struct _SwiftHashingSecretKey _swift_stdlib_Hashing_secretKey;
 SWIFT_RUNTIME_STDLIB_INTERFACE
 __swift_uint64_t _swift_stdlib_HashingDetail_fixedSeedOverride;
 
-struct _SwiftEmptyBoxStorage {
-  struct HeapObject header;
-};
-
-SWIFT_RUNTIME_STDLIB_INTERFACE
-struct _SwiftEmptyBoxStorage _EmptyBoxStorage;
-
 #ifdef __cplusplus
 
 static_assert(std::is_pod<_SwiftEmptyArrayStorage>::value,

stdlib/public/runtime/HeapObject.cpp

@@ -228,6 +228,24 @@ OpaqueValue *swift::swift_projectBox(HeapObject *o) {
   return metadata->project(o);
 }
 
+namespace { // Begin anonymous namespace.
+
+struct _SwiftEmptyBoxStorage {
+  HeapObject header;
+};
+
+swift::HeapLocalVariableMetadata _emptyBoxStorageMetadata;
+
+/// The singleton empty box storage object.
+_SwiftEmptyBoxStorage _EmptyBoxStorage = {
+ // HeapObject header;
+  {
+    &_emptyBoxStorageMetadata,
+  }
+};
+
+} // End anonymous namespace.
+
 HeapObject *swift::swift_allocEmptyBox() {
   auto heapObject = reinterpret_cast<HeapObject*>(&_EmptyBoxStorage);
   SWIFT_RT_ENTRY_CALL(swift_retain)(heapObject);

stdlib/public/stubs/GlobalObjects.cpp

@@ -127,17 +127,6 @@ void swift::_swift_instantiateInertHeapObject(void *address,
   ::new (address) HeapObject{metadata};
 }
 
-swift::HeapLocalVariableMetadata _emptyBoxStorageMetadata;
-
-/// The signleton empty box storage object.
-swift::_SwiftEmptyBoxStorage swift::_EmptyBoxStorage = {
- // HeapObject header;
-  {
-    &_emptyBoxStorageMetadata,
-  }
-};
-
-
 namespace llvm { namespace hashing { namespace detail {
   // An extern variable expected by LLVM's hashing templates. We don't link any
   // LLVM libs into the runtime, so define this here.