[Issue 24018] array concatenation doesn't work with disabled default construction

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24018

Teodor Dutu <teodor.dutu at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |teodor.dutu at gmail.com

--- Comment #2 from Teodor Dutu <teodor.dutu at gmail.com> ---
The old hook was using `__arrayAlloc()` and `__setArrayAllocLength()` to
allocate the resulting array. I am trying to move them to core.lifetime.d as
templates now as part of https://github.com/dlang/dmd/pull/15299. After this,
I'll update `_d_arraycatnTX()` to use them instead of `.length = ...`.

I can't just import them from rt.lifetime.d to core.lifetime.d because the
build system doesn't allow this dependency. And core.lifetime.d is never
compiled, so it can only contain templates. I gave more details about this
issue in this post: https://github.com/dlang/dmd/pull/15299

--