[llvm] [X86] For minsize memset/memcpy, use byte or double-word accesses (PR #87003)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> @phoebewang is this adequate?

Can you split the 2nd commit into one NFC for refactor and one for the change?

https://github.com/llvm/llvm-project/pull/87003