I usually build Python directly in my source repository (the directory
containing the configure script).  Accordingly, I have .o files scattered
throughout my sandbox.

Today I decided to build --with-pydebug, so I created a debug directory,
then ran ../configure from within that directory, giving the arguments
I wanted.  When I ran make it croaked with a link error linking pgen.
The linker complained that tokenizer_pgen.o and pgenmain.o weren't found.

Messing around with make -d I figured out that when make ran it
concluded that Parser/pgenmain.o didn't need to be rebuilt.  It thought
that ../Parser/pgenmain.o satisfied the dependency for Parser/pgenmain.o.
I don't know if this is a problem with GNU make's VPATH processing or
with the dependency specification in Python's makefile.

I can work around the problem by avoiding builds directly in my sandbox
but it would be nice if this worked.

(I'm experiencing a sense of deja vu.  Perhaps I've reported this problem
sometime in the dim, dark past, but I can't find anything searching for
either "VPATH" or "makefile".)