the current yacc rules allow multiple runs to generate the same files. usually
this doesn't come up as the generated files are shipped in the tarball, but
when you modify parse.y (applying a patch or developing or whatever), you can
hit this problem.
simple way of showing this:
make -j y.
the current code generates a bunch of local libraries in subdirs and then
links bash against that. those subdirs sometimes need version.h. so they
have a rule to change back up to the parent dir and build version.h (which is
fine). the trouble is that the top level objects and the subdirs are al
