Documentation re -betterC compatibility with standard library functions

[Dennis]

On Tuesday, 28 January 2025 at 15:00:13 UTC, Jonathan M Davis 
wrote:
> but we provide no guarantees that any code that works with 
> -betterC right now will continue to do so, and we do not intend 
> to add -betterC support. So, if you use something from Phobos 
> that happens to work with -betterC today, it could stop working 
> with -betterC tomorrow if a change is made to fix or improve 
> something, and it's not compatible with -betterC.

There are @betterC unittests in Phobos. Those could be modified, 
but I'd say those unittests give soft guarantees of whatever 
functions they're testing working with -betterC.