package/pkg-autotools.mk: only pass --runstatedir=/run if supported

Fixes:
(thttpd) http://autobuild.buildroot.net/results/f74/f74cae1d981b284a69d7a4e138faf97e45e44865/
(wipe) http://autobuild.buildroot.net/results/4dc/4dc77752d5851d8a71d234c0b284ca696e633754/

And (possibly, unable to reproduce locally):
http://autobuild.buildroot.net/results/658/65882e1f266e818fecef2892c9493d3b8e1e912e/

--runstatedir was added in autoconf 2.69b:
http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commit;h=a197431414088a417b407b9b20583b2e8f7363bd



Some earlier autoconf versions (E.G. 2.13 as used by thttpd/wipe) get
confused if --runstatedir is passed, so only do so if it is supported (E.G.
present in the script).

With this change we can go back to passing --runstatedir instead of
runstatedir, so this effectively reverts commit c28b2703
(package/pkg-autotools.mk: fix runtime path).

Suggested-by: Norbert Lange <nolange79@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>