[PATCH 2/16][ARM] PR/63870 Add __builtin_arm_lane_check.

[Alan Lawrence]

Kyrill Tkachov wrote:
> Hi Alan,
> 
> Can you please add a comment on top of this saying that this builtin only exists to perform the
> lane check, just to make it explicit for the future.

Done, and pushed as r226252.

Charles, thanks for your patience, and I hope this lets you move forwards. I 
realize this leaves you slightly "picking up the pieces" in terms of what's 
there and what isn't, but in theory it corresponds to what we've done previously 
in AArch64 - give me a shout if you are unclear how to proceed!

Thanks, Alan