[llvm] [AMDGPU] Only insert intrinsic declarations when needed (PR #117998)

[Shilei Tian via llvm-commits]

================
@@ -38,6 +38,7 @@ using StackVector = SmallVector<StackEntry, 16>;
 
 class SIAnnotateControlFlow {
 private:
+  Function *F;
----------------
shiltian wrote:

If you add `= nullptr` below, why not these?

https://github.com/llvm/llvm-project/pull/117998