[llvm] [X86] Prevent NUW flag forwarding in ADD->SUB peephole (PR #201612)

[via llvm-commits]

hesam-oxe wrote:

P.S. — the branch is now also **rebased onto current `main`** (`f04117ce`), since three months of drift had left it conflicted. Two of the guarded patterns (the `GR64, 128` → `SUB64ri32` / `SUB64ri32_ND` cases) were removed upstream in the meantime, so they are left deleted; the `0x0000000080000000` block follows main's `HasNDD` predicate rename and keeps the `add_without_nuw` guard. Pre-merge CI is running on the new head.

https://github.com/llvm/llvm-project/pull/201612