[PATCH] FreeBSD AArch64 support

[Tim Northover]

Hi Andrew,

Thanks for adding the tests.

> These should be as described in the AArch64 ABI documentation. There
> should be no need to differ without a good reason.

That's good (I'm not a fan of putting custom tweaks on the documented
ABI, really, though it does happen -- Darwin always has signed char,
for example, no matter what the CPU ABI says).

But I don't think the documented ABI covers everything, and it also
explicitly leaves a few choices to the platform. The key one you'll
want to check is the AAPCS:
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055b/IHI0055B_aapcs64.pdf.

The choices I'm aware of within that document are:
   + what is size_t?
   + What's the status of x18?
   + What frame records do you mandate?
   + How big is wchar_t?

But it's been a while so I may have missed some. Exactly which type
gets to be uint64_t is also ABI-visible (E.g. in C++ name manglings)
but not specifically mentioned.

I've looked at the choices in the test, and they all seem sensible to
me so go ahead and commit if you like.

Cheers.

Tim.