[llvm] [Sink] Fix bugs of sinking unreachable BB from phi (PR #68576)

[Nikita Popov via llvm-commits]

================
@@ -40,3 +39,34 @@ dead:                                             ; preds = %dead
   %and.dead = and i32 undef, %conv
   br label %dead
 }
+
+define i32 @dead_from_phi(i32 noundef %a) #0 {
----------------
nikic wrote:

Drop noundef and `#0`.

https://github.com/llvm/llvm-project/pull/68576