Fixes up dump_syms build on OS X so it works with ELF.

src/common/dwarf/dwarf2reader.cc

 // Copyright (c) 2010 Google Inc. All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 621 matching lines @@
         dwp_byte_reader_.reset(new ByteReader(reader_->GetEndianness()));
         dwp_byte_reader_->SetAddressSize(width);
         dwp_reader_.reset(new DwpReader(*dwp_byte_reader_, elf));
         dwp_reader_->Initialize();
       } else {
         delete elf;
       }
     }
   }
   bool found_in_dwp = false;
-  if (dwp_reader_ != NULL) {
+  if (dwp_reader_) {
     // If we have a .dwp file, read the debug sections for the requested CU.
     SectionMap sections;
     dwp_reader_->ReadDebugSectionsForCU(dwo_id_, &sections);
     if (!sections.empty()) {
       found_in_dwp = true;
       CompilationUnit dwp_comp_unit(dwp_path_, sections, 0,
                                     dwp_byte_reader_.get(), handler_);
       dwp_comp_unit.SetSplitDwarf(addr_buffer_, addr_buffer_length_, addr_base_,
                                   ranges_base_, dwo_id_);
       dwp_comp_unit.Start();
@@ skipping 2072 matching lines @@
                                               uint64 insn_offset) {
   fprintf(stderr,
           "%s: CFI %s at offset 0x%llx in section '%s':"
           " the DW_CFA_restore_state instruction at offset 0x%llx"
           " would clear the CFA rule in effect\n",
           filename_.c_str(), CallFrameInfo::KindName(kind), offset,
           section_.c_str(), insn_offset);
 }
 
 }  // namespace dwarf2reader