MDEV-38989 main.ctype_utf16le SEGV in Ubuntu 26.04 (x86-64-v3)

[dr-m]

• The Jira issue number for this PR is: MDEV-38989

Description

my_utf16le_uni(), my_lengthsp_utf16le(): Instead of wrongly claiming aligned access by invoking uint2korr(), inform the compiler of unaligned access by invoking memcpy(), which will be optimized away.

Release Notes

MariaDB Server could crash due to unaligned access when using the utf16le character set encoding.

How can this PR be tested?

mysql-test/mtr main.ctype_utf16le

Note: Given that IBM AIX is currently detached from https://buildbot.mariadb.org, the only big endian target that we exercise is IBM System Z (s390x).

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

[CLAassistant]

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[dr-m]

https://buildbot.mariadb.org/#/builders/916/builds/8311 has passed the test main.ctype_utf16le:

main.ctype_utf16le                       w4 [ pass ]    534

[abarkov]

The patch is OK to push.