[PATCH] MCJIT SubArch detection support

[Tim Northover]

Hi Renato,

> Should I have added "armv8" as well?

I'd say not yet because nowhere else mentions it at the moment. But I
do wonder whether the whole thing should be opt-out rather than
opt-in. I suppose JIT is generally opt-in on LLVM though, so I'd say
it's OK.

> Ok to commit?

I think so. We'll just have to remember to check that any armv8
patches enable these tests when they come along.

Tim.