Fix gcc warning.

Change-Id: I42dee44f1cee68d83d803174f477b79131a7e109
Reviewed-on: http://codereview.qt.nokia.com/702
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Christian Kandeler <christian.kandeler@nokia.com>

src/libs/glsl/glslsemantic.h

@@ -48,6 +48,8 @@ public:
         ExprResult(const Type *type = 0, bool isConstant = false)
             : type(type), isConstant(isConstant) {}
 
+        ~ExprResult() { }
+
         bool isValid() const {
             if (! type)
                 return false;