configure: Update for autoconf 2.71

alsa-project/alsa-lib pull request #324 was opened from phodina:

Hi, this is an update due to Alpine Linux packaging only `autoconf-2.71-r2` so that the https://github.com/alsa-project/alsa-lib/pull/308 could be tested.

Request URL : https://github.com/alsa-project/alsa-lib/pull/324 Patch URL : https://github.com/alsa-project/alsa-lib/pull/324.patch Repository URL: https://github.com/alsa-project/alsa-lib