MinGW support while building as DLL
__MINGW32__ is appropriate to support for MinGW
diff --git a/include/json/config.h b/include/json/config.h
index 07dae64..8254727 100644
--- a/include/json/config.h
+++ b/include/json/config.h
@@ -39,12 +39,12 @@
#ifdef JSON_IN_CPPTL
#define JSON_API CPPTL_API
#elif defined(JSON_DLL_BUILD)
-#if defined(_MSC_VER) || defined(__GNUC__)
+#if defined(_MSC_VER) || defined(__MINGW32__)
#define JSON_API __declspec(dllexport)
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#endif // if defined(_MSC_VER)
#elif defined(JSON_DLL)
-#if defined(_MSC_VER) || defined(__GNUC__)
+#if defined(_MSC_VER) || defined(__MINGW32__)
#define JSON_API __declspec(dllimport)
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#endif // if defined(_MSC_VER)