Clean up includes in autotools-plugin.

Fixing an lupdate warning about cyclic dependencies of
autotoolsbuildsettingswidget.h.

Change-Id: I0e1c721df2c5f70ae9de38dd9bc5a34b63622ba7
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/autotoolsprojectmanager/autotoolsprojectnode.h

@@ -36,7 +36,10 @@
 #define AUTOTOOLSPROJECTNODE_H
 
 #include <projectexplorer/projectnodes.h>
-#include <coreplugin/idocument.h>
+
+namespace Core {
+class IDocument;
+}
 
 namespace AutotoolsProjectManager {
 namespace Internal {