MDEV-35785: Use same innodb_log_file_mmap description on all systems

MDEV-35785: Use same innodb_log_file_mmap description on all systems

On most 64-bit architectures `mariadbd --help --verbose` said:

    Whether ib_logfile0 resides in persistent memory or
    should initially be memory-mapped

On 32-bit architectures and some 64-bit (e.g. s390x) it said:

    Whether ib_logfile0 should initially be memory-mapped

Having the help test vary with the same source code build with the same
build flags and dependencies seems confusing. Unify the text to always
be the same for clarity.

Ideally the embedded help text would be the exact same first sentence
as the wiki docs[1] but use this custom text now for better clarity.

[1] https://mariadb.com/kb/en/innodb-system-variables/#innodb_log_file_mmap

Forwarded: no

Gbp-Pq: Name MDEV-35785-Use-same-innodb_log_file_mmap-description.patch