[clang] [OpenACC][NFC] Add OpenACC Clause AST Nodes/infrastructure (PR #87675)

[Alexey Bataev via cfe-commits]

================
@@ -94,9 +94,10 @@ StmtResult SemaOpenACC::ActOnEndStmtDirective(OpenACCDirectiveKind K,
   case OpenACCDirectiveKind::Parallel:
   case OpenACCDirectiveKind::Serial:
   case OpenACCDirectiveKind::Kernels:
+    // TODO OpenACC: Add clauses to the construct here.
     return OpenACCComputeConstruct::Create(
         getASTContext(), K, StartLoc, EndLoc,
-        AssocStmt.isUsable() ? AssocStmt.get() : nullptr);
+        /*Clauses=*/{}, AssocStmt.isUsable() ? AssocStmt.get() : nullptr);
----------------
alexey-bataev wrote:

```suggestion
        /*Clauses=*/std::nullopt, AssocStmt.isUsable() ? AssocStmt.get() : nullptr);
```

https://github.com/llvm/llvm-project/pull/87675