8005592: ClassLoaderDataGraph::_unloading incorrectly defined as nonstatic in vmStructs

Summary: Added assertion to catch problem earlier and removed the unused field
Reviewed-by: dholmes, acorn

src/share/vm/runtime/vmStructs.cpp

@@ -717,7 +717,6 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
   nonstatic_field(ClassLoaderData,             _next,                                         ClassLoaderData*)                      \
                                                                                                                                      \
   static_field(ClassLoaderDataGraph,           _head,                                         ClassLoaderData*)                      \
-  nonstatic_field(ClassLoaderDataGraph,        _unloading,                                    ClassLoaderData*)                      \
                                                                                                                                      \
   /*******************/                                                                                                              \
   /* GrowableArrays  */                                                                                                              \
@@ -2575,7 +2574,8 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
 
 // This macro checks the type of a VMStructEntry by comparing pointer types
 #define CHECK_NONSTATIC_VM_STRUCT_ENTRY(typeName, fieldName, type)                 \
- {typeName *dummyObj = NULL; type* dummy = &dummyObj->fieldName; }
+ {typeName *dummyObj = NULL; type* dummy = &dummyObj->fieldName;                   \
+  assert(offset_of(typeName, fieldName) < sizeof(typeName), "Illegal nonstatic struct entry, field offset too large"); }
 
 // This macro checks the type of a volatile VMStructEntry by comparing pointer types
 #define CHECK_VOLATILE_NONSTATIC_VM_STRUCT_ENTRY(typeName, fieldName, type)        \