Break build if using 64-bit integers with ARDUINOJSON_USE_LONG_LONG==0

extras/tests/FailingBuilds/write_long_long.cpp

@@ -0,0 +1,19 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#define ARDUINOJSON_USE_LONG_LONG 0
+#include <ArduinoJson.h>
+
+#if defined(__SIZEOF_LONG__) && __SIZEOF_LONG__ >= 8
+#error This test requires sizeof(long) < 8
+#endif
+
+#if !ARDUINOJSON_HAS_LONG_LONG
+#error This test requires C++11
+#endif
+
+int main() {
+  DynamicJsonDocument doc(1024);
+  doc["dummy"] = static_cast<long long>(42);
+}