[8] RFR: Save vector registers before LRB slowpath call

[Roman Kennke]

>> Have you checked aarch64?
> 
> aarch64 seems to call (push|pop)_call_clobbered_registers, which includes FPU registers.
> Not sure it saves the vector registers, though.

I think it's ok then.

> However, back to x86, I see that this one:
>   https://bugs.openjdk.java.net/browse/JDK-8229977
> 
> ...also saves FPU state. Do we have to do the same here?

Uuuhhhm. I don't actually recall. CAS/CAE doesn't actually use the
LRB-stub as the bug says, or maybe I don't see it. Anyhow, the stub is
not present in 8u, and if it *did* use it somehow, it would go through
the path that you just fixed.

Roman