After I place the libpthread addon in the hurd glibc folder, I need to
rerun autoreconf. But I need exaclty the version 2.68, so I added it.
And because I use the autoconf-wrapper in my glibc/hurd recipe I  changed
it to a procedure that takes an 'autoconf-version' argument to decide which
one to use, so I won't have to duplicate things.