linux: turn on -Wextra

sandbox/linux/seccomp/library.h

 // Copyright (c) 2010 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 LIBRARY_H__
 #define LIBRARY_H__
 
 #include <elf.h>
 #include <functional>
 #include <map>
@@ skipping 108 matching lines @@
       return false;
     }
     *reinterpret_cast<T *>(
         reinterpret_cast<char *>(iter->second.start) + offset) = *value;
     return true;
   }
 
   bool parseElf();
   const Elf_Ehdr* getEhdr();
   const Elf_Shdr* getSection(const string& section);
-  const int getSectionIndex(const string& section);
+  int getSectionIndex(const string& section);
   void makeWritable(bool state) const;
   void patchSystemCalls();
   bool isVDSO() const { return isVDSO_; }
 
  protected:
   bool parseSymbols();
 
  private:
   class GreaterThan : public std::binary_function<Elf_Addr, Elf_Addr, bool> {
     // We create the RangeMap with a GreaterThan rather than the default
@@ skipping 50 matching lines @@
   char*           image_;
   size_t          image_size_;
   static char*    __kernel_vsyscall;
   static char*    __kernel_sigreturn;
   static char*    __kernel_rt_sigreturn;
 };
 
 } // namespace
 
 #endif // LIBRARY_H__