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

public/fpdf_save.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 _FPDFSAVE_H_
 #define _FPDFSAVE_H_
 
 #include "fpdfview.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 
 // Structure for custom file write
-struct FPDF_FILEWRITE{
+typedef struct FPDF_FILEWRITE_ {
 
         //
         //Version number of the interface. Currently must be 1.
         //
         int version;
 
         // 
         // Method: WriteBlock
         //                      Output a block of data in your custom way.
         // Interface Version:
         //                      1
         // Implementation Required:
         //                      Yes
         // Comments:
         //                      Called by function FPDF_SaveDocument
         // Parameters:
         //                      pThis           -       Pointer to the structure itself
         //                      pData           -       Pointer to a buffer to output
         //                      size            -       The size of the buffer.
         // Return value:
         //                      Should be non-zero if successful, zero for error.
         //
-        int             (*WriteBlock)( FPDF_FILEWRITE* pThis, const void* pData, unsigned long size);
+        int             (*WriteBlock)(struct FPDF_FILEWRITE_* pThis, const void* pData, unsigned long size);
 
-};
+} FPDF_FILEWRITE;
 
 
 /** @brief Incremental. */
 #define FPDF_INCREMENTAL                1
 /** @brief No Incremental. */
 #define FPDF_NO_INCREMENTAL             2
 /** @brief Remove security. */
 #define FPDF_REMOVE_SECURITY    3
 
 // Function: FPDF_SaveAsCopy
@@ skipping 19 matching lines @@
 //                      TRUE if succeed, FALSE if failed.
 //
 DLLEXPORT FPDF_BOOL STDCALL FPDF_SaveWithVersion(FPDF_DOCUMENT document,FPDF_FILEWRITE * pFileWrite,
         FPDF_DWORD flags, int fileVersion);
 
 #ifdef __cplusplus
 };
 #endif
 
 #endif //_FPDFSAVE_H_