build: use --runstatedir instead of --localstatedir

build: use --runstatedir instead of --localstatedir

The util-linux code was previously aligned to use @localstatedir@ and
the util-linux build system was set to override the default to use /run.

Current GNU Coding Standards introduced the @runstatedir@ variable
for this purpose. Lets use that instead.

The GNU default for @runstatedir@ is ${localstatedir}/run so util-linux
still override the default to be /run to preserve the status quo from
before. The only difference is that you'll now pass --runstatedir to
override the location on the command line instead of --localstatedir.

(FWIW, Debhelper in compat 11 will automatically start passing
--runstatedir=/run to all autotools configured builds. It already
passes --localstatedir=/var (to avoid it ending up with the GNU default
/usr/local/var) which breaks the util-linux build system code that
tries to default it to /run. This change will thus allow util-linux
and debhelper to work better together and avoid the need for a
package-specific override.)

Relevant historic commits:
 * commit 07a16b9d1e5a48550a0d19abb9a900853433ffa2
   "build-sys: change --localstatedir to /run"
 * commit 80c51185d50f00a2701f9379f10fc48a0f885dfc
   "uuidd: use run configured state directory"
 * commit 01c5b787947aeaffc7e56000827e3edefa357c59
   "agetty: use configured run state directory"

[kzak@redhat.com: - add $runstatedir fallback for autoconf < 2.70
                  - check for unmodified $localstatedir]

CC: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Karel Zak <kzak@redhat.com>