The patch is ready for review in the branch bb-10.5-MDEV-24115

ifdefs aren't particularly good for maintainability and readability. Why not to cast unconditionally? Or to use uint for the constructor argument?

Timeval is widely used across the source code and some of methods (e.g. Field::store_timestamp)
call Timeval constructor passing its arguments directly to constructor's arguments that results in
implicit dependency of Timeval constructor's arguments on type of calling method's arguments (Field::store_timestamp in our case).

Changing types of argument in every method that calls Timeval constructor requires more changes than just one cast inside constructor of Timeval
So, from my point of view it is better to cast unconditionally to uint inside Tmeval constructor.

ok. by "cast unconditionally" I meant

-    tv_usec= usec;

+    tv_usec= (suseconds_t)usec;

although uint might work too

The type suseconds_t conforms to POSIX.1-2001 and later.
Release edition POSIX.1-2001 confused me a bit and therefore I proposed casting to uint.
Now I rechecked manual pages and found that timeval is also declared conforming to POSIX.1-2001 and later.
Since timeval struct is widely and successfully used both in MariaDB and MySQL I believe that we can
suppose that every environment where MariaDB can be used should conform to POSIX.1-2001.
So, I agree with your remark and will change casting type from uint to suseconds_t.