In some cases LLVM (especially the SLP vectorizer) will create vectors
that are 256 bytes (or larger). Given that this is intentional[0] is
likely to get more common, this patch updates the StackMap binary
format to deal with the spill locations for said vectors.
This change also bumps the stack map version from 2 to 3.
It's really unfortunate that we had to grow the size so much here, but given this is intended to be immediately parsed and thrown away, I guess it's not too much of a problem.