pdfium: Fix all -Wdelete-non-virtual-dtor violations on Mac.

core/include/fxcrt/fx_system.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 _FX_SYSTEM_H_
 #define _FX_SYSTEM_H_
 #define _FX_WIN32_DESKTOP_              1
 #define _FX_LINUX_DESKTOP_              4
@@ skipping 257 matching lines @@
 FX_INT64        FXSYS_wtoi64(FX_LPCWSTR str);
 FX_LPCSTR       FXSYS_i64toa(FX_INT64 value, FX_LPSTR str, int radix);
 FX_LPCWSTR      FXSYS_i64tow(FX_INT64 value, FX_LPWSTR str, int radix);
 int                     FXSYS_round(FX_FLOAT f);
 #define         FXSYS_Mul(a, b) ((a) * (b))
 #define         FXSYS_Div(a, b) ((a) / (b))
 #define         FXSYS_MulDiv(a, b, c) ((a) * (b) / (c))
 #define         FXSYS_sqrt2(a, b) (FX_FLOAT)FXSYS_sqrt((a)*(a) + (b)*(b))
 #ifdef __cplusplus
 };
+
+#if defined(__clang__) || defined(_MSC_VER)
+#define FX_FINAL final
+#elif defined(__GNUC__) && __cplusplus >= 201103 && \
+      (__GNUC__ * 10000 + __GNUC_MINOR__ * 100) >= 40700
+#define FX_FINAL final
+#else
+#define FX_FINAL
 #endif
 #endif
+#endif