Avoid warning on empty expressions

For some reason, Q_UNUSED includes already a semicolon, adding one
on the user side creates an additional empty statement.

Change-Id: I9c5e8fac381345a60792cb75e2938fd53958d3b0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/autotoolsprojectmanager/autotoolsproject.cpp

@@ -220,7 +220,7 @@ void AutotoolsProject::makefileParsingFinished()
 
 void AutotoolsProject::onFileChanged(const QString &file)
 {
-    Q_UNUSED(file);
+    Q_UNUSED(file)
     loadProjectTree();
 }