databases/mariadb106-server: fix build on powerpc64*

/wrkdirs/usr/ports/databases/mariadb106-client/work/mariadb-10.6.18/mysys/crc32/crc32c.cc:498:7: error: use of undeclared identifier 'arch_ppc_probe'

498 |   if (arch_ppc_probe())
    |       ^

1 error generated.