QtSupport: Fix compilation with Qt 4.

Introduced by b57fd371095c4c5b81864fba90b397e160b2fa88 .

Change-Id: Ie09c764408bbe4ed1e2011cbf809aa05808cd583
Reviewed-by: Robert Loehning <robert.loehning@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>