Add more context to aix_externcpp1 selection to ensure
that the fix is correctly applied even in future AIX versions.
fixincludes/Changelog:
2021-07-01 Clément Chigot <clement.chigot@atos.net>
* inclhack.def (aix_externcpp1): Improve select regexp.
* fixincl.x: Regenerate.
* tests/base/sys/socket.h: Update.
(cherry picked from commit 03b634c8e0)
