ProjectExplorer: Consolidate setup of build dir aspect

This is getting repetitive.

There's a new connect too, that's not wrong in the current two uses
and will be helpful in the upcoming Qbs one.

Change-Id: I4a4923a43937922c66be1f73822103b1e3e7b077
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/projectexplorer/buildconfiguration.h

@@ -101,6 +101,7 @@ public:
 
     ProjectExplorer::BaseStringAspect *buildDirectoryAspect() const;
     void setConfigWidgetDisplayName(const QString &display);
+    void setBuildDirectoryHistoryCompleter(const QString &history);
 
 signals:
     void environmentChanged();