Fix compilation with clang

src/x64/full-codegen-x64.cc

 // Copyright 2012 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 4822 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 
 static const byte kJnsInstruction = 0x79;
 static const byte kJnsOffset = 0x1d;
-static const byte kCallInstruction = 0xe8;
 static const byte kNopByteOne = 0x66;
 static const byte kNopByteTwo = 0x90;
+#ifdef DEBUG
+static const byte kCallInstruction = 0xe8;
+#endif
 
 
 void BackEdgeTable::PatchAt(Code* unoptimized_code,
                             Address pc,
                             BackEdgeState target_state,
                             Code* replacement_code) {
   Address call_target_address = pc - kIntSize;
   Address jns_instr_address = call_target_address - 3;
   Address jns_offset_address = call_target_address - 2;
 
@@ skipping 50 matching lines @@
 
   ASSERT_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64