Avoid redundent redefinition of __STDC_FORMAT_MACROS when building with clang

src/mips64/constants-mips64.h

 // Copyright 2012 the V8 project 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  V8_MIPS_CONSTANTS_H_
 #define  V8_MIPS_CONSTANTS_H_
 
 // UNIMPLEMENTED_ macro for MIPS.
 #ifdef DEBUG
 #define UNIMPLEMENTED_MIPS()                                                  \
@@ skipping 54 matching lines @@
 #elif(defined(__mips_soft_float) && __mips_soft_float != 0)
 // This flag is raised when -msoft-float is passed to the compiler.
 // Although FPU is a base requirement for v8, soft-float ABI is used
 // on soft-float systems with FPU kernel emulation.
 const bool IsMipsSoftFloatABI = true;
 #else
 const bool IsMipsSoftFloatABI = true;
 #endif
 
 
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif
 #include <inttypes.h>
 
 
 // Defines constants and accessor classes to assemble, disassemble and
 // simulate MIPS32 instructions.
 //
 // See: MIPS32 Architecture For Programmers
 //      Volume II: The MIPS32 Instruction Set
 // Try www.cs.cornell.edu/courses/cs3410/2008fa/MIPS_Vol2.pdf.
 
@@ skipping 779 matching lines @@
 
 // TODO(plind): below should be based on kPointerSize
 // TODO(plind): find all usages and remove the needless instructions for n64.
 const int kCArgsSlotsSize = kCArgSlotCount * Instruction::kInstrSize * 2;
 
 const int kBranchReturnOffset = 2 * Instruction::kInstrSize;
 
 } }   // namespace v8::internal
 
 #endif    // #ifndef V8_MIPS_CONSTANTS_H_