ARM atomics overhaul for musl

[Rich Felker]

On Sun, Nov 16, 2014 at 10:27:04AM -0800, Andy Lutomirski wrote:
> Would it make sense for arm and arm64 to add bits for these features
> to AT_HWCAP, along with an extra bit indicating that the kernel
> provides these bits?

Sadly since it wasn't available there from the beginning, I don't
think there would be a lot of benefit in adding it now, but it
wouldn't hurt.

It might be useful if there's a risk that the existing methods will
break in the future; adding it now would ensure that there are only a
known finite set of kernels for which the old hackish string methods
need to be used, so that there's no concern about their compatibility
with future kernels/models.

Rich