Fix unknown pragma warning for non-MSVC compilers

Author: ras0219-msft

Release/libs/websocketpp/websocketpp/connection.hpp

@@ -161,10 +161,12 @@ typedef lib::function<void(lib::error_code const & ec)> write_frame_handler;
      * @todo Move this to configs to allow compile/runtime disabling or enabling
      * of protocol versions
      */
+#if defined(_MSC_VER)
 #pragma warning(push)
 #pragma warning(disable : 4592)
     static std::vector<int> const versions_supported = {0,7,8,13};
 #pragma warning(pop)
+#endif
 #else
     /// Helper array to get around lack of initializer lists pre C++11
     static int const helper[] = {0,7,8,13};