[llvm] [LowerBufferFatPointers] Don't lose data from unaligned < word vectors (PR #132981)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

Update on the motivating circumstances for this patch:

We *might* want to implement `llvm.intr.masked.load` in the backend instead of going down this route, since we can expect most loads won't be trying to read off the end of a buffer.

https://github.com/llvm/llvm-project/pull/132981