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

[Aaron Ballman via cfe-commits]

================
@@ -9727,6 +9727,51 @@ static TypedefDecl *CreateHexagonBuiltinVaListDecl(const ASTContext *Context) {
   return Context->buildImplicitTypedef(VaListTagArrayType, "__builtin_va_list");
 }
 
+static TypedefDecl *
+CreateXtensaABIBuiltinVaListDecl(const ASTContext *Context) {
+  // typedef struct __va_list_tag {
+  RecordDecl *VaListTagDecl;
+
+  VaListTagDecl = Context->buildImplicitRecord("__va_list_tag");
+  VaListTagDecl->startDefinition();
+
+  const size_t NumFields = 3;
----------------
AaronBallman wrote:

```suggestion
  constexpr size_t NumFields = 3;
```

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