[clang] [Clang][Xtensa] Add Xtensa target. (PR #118008)

[Eli Friedman via cfe-commits]

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@@ -358,7 +358,10 @@ class TargetInfo : public TransferrableTargetInfo,
     //    void *__saved_reg_area_end_pointer;
     //    void *__overflow_area_pointer;
     //} va_list;
-    HexagonBuiltinVaList
+    HexagonBuiltinVaList,
+
+    // Tensilica Xtensa
+    XtensaABIBuiltinVaList
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efriedma-quic wrote:

It would be helpful to stick a brief definition of the structure in a comment here, for comparison,

https://github.com/llvm/llvm-project/pull/118008