[clang] [Clang] Treat `ext_vector_type` as a regular type attribute (PR #130177)

[Joseph Huber via cfe-commits]

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@@ -1721,17 +1721,10 @@ def EnableIf : InheritableAttr {
   let Documentation = [EnableIfDocs];
 }
 
-def ExtVectorType : Attr {
-  // This is an OpenCL-related attribute and does not receive a [[]] spelling.
-  let Spellings = [GNU<"ext_vector_type">];
-  // FIXME: This subject list is wrong; this is a type attribute.
-  let Subjects = SubjectList<[TypedefName], ErrorDiag>;
+def ExtVectorType : TypeAttr {
+  let Spellings = [RegularKeyword<"__vector_type">, GNU<"ext_vector_type">];
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jhuber6 wrote:

That was my preference as well. I went ahead and kept the keyword with the `ext_vector_type` spelling since that *should* resolve cases where we're worried about double parsing. Should I just keep it as just `clang`?

https://github.com/llvm/llvm-project/pull/130177