[PATCH] atomic: Reinstate HAVE_64B_ATOMICS configure check

[Wilco Dijkstra]

Hi Adhemerval,

> Last time I checked I saw that some old gcc versions are not showing the
> expected results on some ABIs (for instance Ubuntu gcc 13 on armhf). I
> am not sure how to properly handle it.

Which case do you mean? On armv7-a 64-bit atomics are always supported,
so I don't see how it could fail (godbolt confirms it's fine on all released GCC
versions from 13.1 to 15.1)... However even if it was turned off in some weird
configuration, it would be the same as it was before with 64-bit atomics
disabled by default on all 32-bit targets.

Cheers,
Wilco