use restrict keyword in c++

include/ua_config.h.in

@@ -78,6 +78,8 @@
 /* Define non-aliasing pointers */
 #ifdef _MSC_VER
 # define UA_RESTRICT __restrict
+#elif defined(__GNUC__)
+# define UA_RESTRICT __restrict__
 #else
 # define UA_RESTRICT restrict
 #endif