[stable] core.atomic: Make type repainting in atomicLoad cheaper

[kinke]

Pinging @TurkeyMan.

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[TurkeyMan]

How does this make it cheaper? Why isn't this identical?
I'm not on board with this change... I specifically designed against instantiations of the implementation functions with types like that.

[TurkeyMan]

Oh I get it, because move is rubbish...
We need to fix move... it's my #1 slot for worst problem in D right now.

[kinke]

On I get it, because move is rubbish...

Exactly, and I don't see how T is better suited for the internal implementation than the TailShared!T; it's not like you'd use an integer type of matching size here or something like that.

The actual reason is that LDC's druntime testrunner wouldn't link due to undefined move template instantiations without this; this rewrite hides that problem at least. ;)

[TurkeyMan]

Well, TailShared should be eradicated somehow, and I'm trying to isolate that as much as possible for the time being.
I guess I can tolerate this patch though, since it's contained in a function that shouldn't exist anyway (see the comment immediately above). It still upsets me :/

[PetarKirov]

@wilzbach is @dlang-bot taking a day off? :D