Define "__STDC_FORMAT_MACROS" for using PRI{u,x}64 in C++.

Summary: Closes https://github.com/facebook/folly/pull/467

Reviewed By: yfeldblum

Differential Revision: D3787151

Pulled By: Orvid

fbshipit-source-id: e255c9daea9917082f684e52e27984770c9f08b1

folly/test/ConvTest.cpp

@@ -14,11 +14,16 @@
  * limitations under the License.
  */
 
+#ifndef __STDC_FORMAT_MACROS
+#define __STDC_FORMAT_MACROS 1
+#endif
+
 #include <boost/lexical_cast.hpp>
 #include <folly/Conv.h>
 #include <folly/Foreach.h>
 #include <gtest/gtest.h>
 #include <algorithm>
+#include <cinttypes>
 #include <limits>
 #include <sstream>
 #include <stdexcept>

folly/test/StringTest.cpp

@@ -14,8 +14,14 @@
  * limitations under the License.
  */
 
+#ifndef __STDC_FORMAT_MACROS
+#define __STDC_FORMAT_MACROS 1
+#endif
+
 #include <folly/String.h>
 
+#include <cinttypes>
+
 #include <boost/regex.hpp>
 #include <gtest/gtest.h>