CMake: Define an "install" target

Change-Id: I036ddc3bfb91fc3a5a9e8923db2befbf60e89a77
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildstep.h

@@ -79,6 +79,8 @@ public:
 
     static QString cleanTarget();
     static QString allTarget();
+    static QString installTarget();
+    static QStringList specialTargets();
 
 signals:
     void cmakeCommandChanged();