[tlbuild] build with non-standard TL_WORKDIR fails in luatexdir

[Vladimir Volovich]

"KB" == Karl Berry writes:

 KB>     I see the problem when using the following Build wrapper:
 KB> Thanks.  I will try to reproduce as soon as I have a chance.
 KB> Unfortunately that may be a little while.  If you or anyone feels
 KB> like delving further, go for it :).

the file web2c/luatexdir/depend.mk contains hardwired dependencies such
as

lua/psout.o: lua/psout.c ../../../../texk/web2c/luatexdir/avl.h mplib.h \
  mpmp.h mppsout.h

which assume a specific layout for the build, instead of using $(srcdir)
etc.

Best,
v.