build: support customization of runstatedir variable with old autoconf

build: support customization of runstatedir variable with old autoconf

Many distros have moved /var/run to /run with the introduction of
systemd. /var/run still exists as a symlink to /run, but its usage
is deprecated.

autoconf added a --runstatedir option back in 2013 but there's still no
new release of autoconf that includes this.

gnulib meanwhile added support to propagate this arg's value to
configmake.h, but it falls back to $localstatedir/run for autoconf 2.69
and older, which is what every distro today has.

To deal with this problem we add a --with-runstatedir arg that then sets
the $runstatedir env variable that future autoconf's --runstatedir arg
will also use. This finally enables $runstatedir to be pointed to /run.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>