[llvm] [DFAJumpThreading] Handle select unfolding when user phi is not a dir… (PR #109511)

[via llvm-commits]

================
@@ -300,3 +300,237 @@ define void @self-reference() {
 end:
   ret void
 }
+
+ at a = external dso_local global ptr, align 8
----------------
XChy wrote:

```suggestion
@a = external global ptr, align 8
```

https://github.com/llvm/llvm-project/pull/109511