Avoid redundent redefinition of __STDC_FORMAT_MACROS when building with clang

R=jochen@chromium.org, paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/404333003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22554 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm64/constants-arm64.h

@@ -15,7 +15,9 @@ STATIC_ASSERT(sizeof(1L) == sizeof(int64_t));      // NOLINT(runtime/sizeof)
 
 
 // Get the standard printf format macros for C99 stdint types.
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif
 #include <inttypes.h>
 
 

src/mips64/constants-mips64.h

@@ -72,7 +72,9 @@ const bool IsMipsSoftFloatABI = true;
 #endif
 
 
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif
 #include <inttypes.h>