Include version in AC_PACKAGE_TARNAME

`AC_PACKAGE_TARNAME` is used by autoconf to generate the default value
of docdir, which we now set to include a version number (see #11354).
This fixed #11659.

Test Plan: `./configure --help`, validate

Reviewers: austin, thomie, hvr, erikd

Reviewed By: hvr, erikd

Subscribers: erikd

Differential Revision: https://phabricator.haskell.org/D1983

GHC Trac Issues: #11659