Fixing ifdef with HAVE_ATOMIC_INTPTR_T

Author: ktakashi

src/sagittarius/private/atomic.h

@@ -71,11 +71,7 @@ typedef struct SgAtomicRefRec
   SgAtomicType type;
   union {
     atomic_long fixnum;
-#ifdef HAVE_ATOMIC_INTPTR_T
-    atomic_intptr_t object;
-#else
-    atomic_size_t object;
-#endif
+    atomic_object_t object;
   } reference;
 
 } SgAtomic;