Make (and verify) public/ files compile under C.

public/fpdf_ext.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef _FPDF_EXT_H_
 #define _FPDF_EXT_H_
 
 #ifndef _FPDFVIEW_H_
@@ skipping 35 matching lines @@
         *                       1
         * Implementation Required:
         *                       Yes
         * Parameters:
         *               pThis           -       Pointer to the interface structure itself.
         *               nType           -       The type of unsupportObject
         *       Return value:
         *               None.
         * */
 
-        void(*FSDK_UnSupport_Handler)(_UNSUPPORT_INFO* pThis,int nType);
-}UNSUPPORT_INFO;
+        void(*FSDK_UnSupport_Handler)(struct _UNSUPPORT_INFO* pThis, int nType);
+} UNSUPPORT_INFO;
 
 
 /**
  * Function: FSDK_SetUnSpObjProcessHandler
  *                       Setup A UnSupport Object process handler for foxit sdk. 
  * Parameters:
  *                      unsp_info               -       Pointer to a UNSUPPORT_INFO structure.
  * Return Value:
  *                      TRUE means successful. FALSE means fails. 
  **/
@@ skipping 31 matching lines @@
  *                      doc             -       Handle to document. Returned by FPDF_LoadDocument function.
  * Return Value:
  *                      The flags for page mode.
  **/
 DLLEXPORT int FPDFDoc_GetPageMode(FPDF_DOCUMENT document);
 
 #ifdef __cplusplus
 };
 #endif
 #endif