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

[Erich Keane via cfe-commits]

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@@ -30,13 +31,23 @@ class OpenACCConstructStmt : public Stmt {
   /// the directive.
   SourceRange Range;
 
-  // TODO OPENACC: Clauses should probably be collected in this class.
+  /// The list of clauses.  This is stored here as an ArrayRef, as this is the
+  /// most convienient place to access the list, however the list itself should
+  /// be stored in leaf nodes, likely in trailing-storage.
+  MutableArrayRef<const OpenACCClause *> Clauses;
 
 protected:
   OpenACCConstructStmt(StmtClass SC, OpenACCDirectiveKind K,
                        SourceLocation Start, SourceLocation End)
       : Stmt(SC), Kind(K), Range(Start, End) {}
 
+  // Used only for initialization, the leaf class can initialize this to
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erichkeane wrote:

This ends up being necessary because the trailing storage isn't initialized when we do construction, so the derived classes need to set this after this class is constructed (and their trailing storage base is legal to do stuff with).

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