CMake: Fix crash when building a cmake project

Reported by Loaden via mail.

Change-Id: I21a9f2ee5787d9271d20f9ed65786d8c7be08d3c
Reviewed-by: Robert Loehning <robert.loehning@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/projectexplorer/abstractprocessstep.cpp

@@ -344,6 +344,11 @@ void AbstractProcessStep::stdError(const QString &line)
     emit addOutput(line, BuildStep::ErrorOutput, BuildStep::DontAppendNewline);
 }
 
+QFutureInterface<bool> *AbstractProcessStep::futureInterface() const
+{
+    return m_futureInterface;
+}
+
 void AbstractProcessStep::checkForCancel()
 {
     if (m_futureInterface->isCanceled() && m_timer->isActive()) {