[clang] [Attributes] Support Attributes being declared as supporting an experimental late parsing mode "extension" (PR #88596)

[Yeoul Na via cfe-commits]

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@@ -2101,9 +2173,21 @@ bool PragmaClangAttributeSupport::isAttributedSupported(
     return SpecifiedResult;
 
   // Opt-out rules:
-  // An attribute requires delayed parsing (LateParsed is on)
-  if (Attribute.getValueAsBit("LateParsed"))
+
+  // An attribute requires delayed parsing (LateParsed is on).
+  switch (getLateAttrParseKind(&Attribute)) {
+  case LateAttrParseKind::Never:
+    break;
+  case LateAttrParseKind::Standard:
+    return false;
+  case LateAttrParseKind::ExperimentalExt:
+    // FIXME: fix this comment
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rapidsna wrote:

^^ so you won't miss this FIXME

https://github.com/llvm/llvm-project/pull/88596