[StackMaps] Increase the size of the "location size" field

Summary:
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.

[0]: https://reviews.llvm.org/D32533#738350

Reviewers: reames, kavon, skatkov, javed.absar

Subscribers: mcrosier, nemanjai, llvm-commits

Differential Revision: https://reviews.llvm.org/D32629

llvm-svn: 301615