ProjectManager: Simplify Project::setBuildSystemCreator()

Make it a template method.

Change-Id: I3f0510c89d7f0bfe2f814dadc4d8de01c0e1cc89
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/workspaceproject.cpp

@@ -262,7 +262,7 @@ public:
 
         setId(Id::fromString(WORKSPACE_PROJECT_ID));
         setDisplayName(projectDirectory().fileName());
-        setBuildSystemCreator([](Target *t) { return new WorkspaceBuildSystem(t); });
+        setBuildSystemCreator<WorkspaceBuildSystem>();
     }
 
     FilePath projectDirectory() const override