Fixed build on Mac, where g++ is a bit too dumb to see that a variable is always initialized.

src/ia32/code-stubs-ia32.cc

 // Copyright 2011 the V8 project authors. 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 in the documentation and/or other materials provided
@@ skipping 515 matching lines @@
 }
 
 
 const char* TypeRecordingUnaryOpStub::GetName() {
   if (name_ != NULL) return name_;
   const int kMaxNameLength = 100;
   name_ = Isolate::Current()->bootstrapper()->AllocateAutoDeletedArray(
       kMaxNameLength);
   if (name_ == NULL) return "OOM";
   const char* op_name = Token::Name(op_);
-  const char* overwrite_name;
+  const char* overwrite_name = NULL;  // Make g++ on Mac happy.
   switch (mode_) {
     case UNARY_NO_OVERWRITE: overwrite_name = "Alloc"; break;
     case UNARY_OVERWRITE: overwrite_name = "Overwrite"; break;
   }
 
   OS::SNPrintF(Vector<char>(name_, kMaxNameLength),
                "TypeRecordingUnaryOpStub_%s_%s_%s",
                op_name,
                overwrite_name,
                TRUnaryOpIC::GetName(operand_type_));
@@ skipping 5445 matching lines @@
   // Do a tail call to the rewritten stub.
   __ jmp(Operand(edi));
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32