[X86] combineConcatVectorOps - only concatenate single-use subops

We could maybe extend this by allowing the lowest subop to have multiple uses and extract the lowest subvector result of the concatenated op, but let's just get the fix in first.

Fixes #67333

GitOrigin-RevId: 04b403d8cc6990171ca0d9bd8d1571e56d231a4d
6 files changed