bsd.lib.mk does not add OBJS etc to CLEANFILES so does not automatically
get them flagged as .NOPATH.  This hurts people who don't use obj dirs.
Since its clean target seprate rm's for things, use NOPATH_FILES as list
to collect things that need .NOPATH.

bsd.obj.mk will add CLEANFILES to NOPATH_FILES and do the deed if needed.

Reviewed by: sbruno