[llvm] [X86] Prevent APX NDD compression when it creates a partial write (PR #132051)

[Daniel Zabawa via llvm-commits]

daniel-zabawa wrote:

note the tests are split over two files because I was hitting errors when RUN lines produced both MIR and asm output, which is likely not a common usage for update_mir_test_checks.  If there's a better way to handle that I'd be glad to learn it. 

https://github.com/llvm/llvm-project/pull/132051