[llvm] [PatternMatch] Do not accept undef elements in m_AllOnes() and friends (PR #88217)

[Yingwei Zheng via llvm-commits]

================
@@ -2983,7 +2983,7 @@ define i8 @signum_i8_i8_use3(i8 %x) {
   ret i8 %r
 }
 
-; poison/undef is ok to propagate in shift amount
+; poison/poison is ok to propagate in shift amount
----------------
dtcxzyw wrote:

```suggestion
; poison is ok to propagate in shift amount
```


https://github.com/llvm/llvm-project/pull/88217