Fix test_util_file for VS2013 too, but skip all the tests for anything older than that because the limitations are too inconvenient.

tests/test_util_file.c

@@ -19,6 +19,7 @@
 
 #include "json.h"
 #include "json_util.h"
+#include "snprintf_compat.h"
 
 static void test_read_valid_with_fd(const char *testdir);
 static void test_read_valid_nested_with_fd(const char *testdir);