[llvm] [IR] Require that ptrmask mask matches pointer index size (PR #69343)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

> This is also the behavior we want for CHERI architectures.

That's not how we think of it; we think of it as "the mask is extended to the index size and applies only to the index"; there are never any 128-bit integers involved, whether abstractly or not. Note that we do not support ptrtoint/inttoptr of capabilities in a preserving way; they give you only the address portion (/ give you a capability with all-zero metadata).

https://github.com/llvm/llvm-project/pull/69343