Avoid redefinition of  __STDC_FORMAT_MACROS.

Change-Id: I5c65ea196bb9a197a74899ceb53543f289f6d494
diff --git a/libbacktrace/BacktraceImpl.cpp b/libbacktrace/BacktraceImpl.cpp
index 39296b4..8027d86 100644
--- a/libbacktrace/BacktraceImpl.cpp
+++ b/libbacktrace/BacktraceImpl.cpp
@@ -21,7 +21,6 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#define __STDC_FORMAT_MACROS
 #include <inttypes.h>
 
 #include <string>