Correction to r3941 to fix mac build-breaker in src/image.cpp (and odd linux bb in samples/exiv2json.cpp)

samples/exiv2json.cpp

@@ -3,6 +3,7 @@
 // Sample program to print metadata in JSON format
 
 #include <exiv2/exiv2.hpp>
+#include <exiv2/datasets.hpp>
 #include "Jzon.h"
 
 #include <iostream>

src/image_int.hpp

@@ -38,6 +38,8 @@
 
 #if (defined(__GNUG__) || defined(__GNUC__)) && ! defined(__clang__)
 #define ATTRIBUTE_FORMAT_PRINTF __attribute__((format(printf, 1, 0)))
+#else
+#define ATTRIBUTE_FORMAT_PRINTF
 #endif
 
 // *****************************************************************************