| I don't like making everything relative to BSDSRCDIR, because it means
| that other code can't use this mechanism.  Say I have another project
| that uses BSD-style makefiles but doesn't use BSDSRCDIR, and I want to
| use EXCLUDE_SUBDIRS.

I'm a little concerned about it.

From my perspective, I would uswe this when I'm in the same CWD
as a Makefile and want to restrict its descent. I don't know necessarily
want to know where it really was in the hierarchy, and I might even
have moved the directory out of the hierarchy. I get the feeling
that this would not let me do:

     cd sys/arch/i386/stand
     make EXCLUDE_SUBDIRS=installboot

which is what I guess I'd like this to do.

--jhawk