Add version-specific defines for each C interface.

ppapi/c/ppb_var.h

 /* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef PPAPI_C_PPB_VAR_H_
 #define PPAPI_C_PPB_VAR_H_
 
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_macros.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/c/pp_var.h"
 
-#define PPB_VAR_INTERFACE "PPB_Var;0.5"
+#define PPB_VAR_INTERFACE_0_5 "PPB_Var;0.5"
+#define PPB_VAR_INTERFACE PPB_VAR_INTERFACE_0_5
 
 /**
  * @file
  * This file defines the PPB_Var struct.
  */
 
 /**
  * @addtogroup Interfaces
  * @{
  */
@@ skipping 50 matching lines @@
    * will be to random memory.
    */
   const char* (*VarToUtf8)(struct PP_Var var, uint32_t* len);
 };
 /**
  * @}
  */
 
 #endif  /* PPAPI_C_PPB_VAR_H_ */