[llvm] [Xtensa] Implement vararg support. (PR #117126)

[Matt Arsenault via llvm-commits]

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@@ -43,12 +44,18 @@ class XtensaMachineFunctionInfo : public MachineFunctionInfo {
   unsigned getVarArgsFirstGPR() const { return VarArgsFirstGPR; }
   void setVarArgsFirstGPR(unsigned GPR) { VarArgsFirstGPR = GPR; }
 
-  int getVarArgsOnStackFrameIndex() const { return VarArgsStackOffset; }
-  void setVarArgsOnStackFrameIndex(int Offset) { VarArgsStackOffset = Offset; }
+  unsigned getVarArgsOnStackFrameIndex() const {
+    return VarArgsOnStackFrameIndex;
+  }
+  void setVarArgsOnStackFrameIndex(unsigned FI) {
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arsenm wrote:

```suggestion
  void setVarArgsOnStackFrameIndex(int FI) {
```

https://github.com/llvm/llvm-project/pull/117126