clear warnings for io_setup failure

While importing MariaDB 11.8.3 into Debian, I noticed that the mariadb-test-run on ppc64el and s390x fail as a lot of the tests emit a new warning that was introduced in https://github.com/MariaDB/server/commit/a87bb96ecb1234c1a1aa4bb6d4b6afe08fd13db9 by marko.

Example log https://launchpadlibrarian.net/809896691/buildlog_ubuntu-questing-s390x.mariadb_1%3A11.8.3-1~bpo25.10.1~1754613936.d96f3f9e83e+import.11.8.3_BUILDING.txt.gz

main.stat_tables_rbr                     w5 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2025-08-08 01:29:55

line

2025-08-08  1:29:54 0 [Warning] InnoDB: native AIO failed: falling back to innodb_use_native_aio=OFF

^ Found warnings in /<<PKGBUILDDIR>>/builddir/mysql-test/var/5/log/mysqld.1.err

ok

In Debian we are only using uring and not libaio at all. The build stage emits:

-- Found URING: /usr/lib/s390x-linux-gnu/liburing.so

-- Could NOT find LIBAIO (missing: LIBAIO_LIBRARIES LIBAIO_INCLUDE_DIRS)

Something in the logic that checks if libaio or uring is available seems to have different behavior on s390x and ppc64el, and ends up emitting this warning all the time, even though libaio wasn't compiled and what the setting of new 'innodb-linux-aio' or old 'innodb_use_native_aio' is won't actually affect anything.