Fix build.xml: Processed CL stub_includes _must_ reside in current folder (make) due to relative fileset access only!

Commit aac4c5fc4ab7c77eff3b71f518100dd182ec2c33 moved processed CL stub_includes
to 'build/includes', which would be 'nice to have'.

However, due to relative fileset restrictions, we must locate it from current folder 'make'.

Not detected, since an old 'make/includes/CL' was still around.

Using dedicated folder 'make/stub_includes.gen'.