need access to Makefile path

[Dave Yost]

Consider a Makefile that starts thus:

    include ../../../Makefile-master

It would be nice if this included Makefile-master knew where it was, so it 
could do stuff like this:

    root := $(MAKEFILE-PARENT-DIR)
    
    classesDir := $(root)/classes

I use this unsatisfactory workaround:

Makefile:

    root := ../../..
    include Makefile-master

Makefile-master:

    classesDir := $(root)/classes


A shell script can know where it is and what its name is.  The same should be 
true for Makefiles.

Thanks

Dave