[clang] [clang] support Wold-style-declaration (PR #78837)

[Aaron Ballman via cfe-commits]

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@@ -4140,12 +4143,14 @@ void Parser::ParseDeclarationSpecifiers(
       }
       isInvalid = DS.setFunctionSpecExplicit(ExplicitLoc, PrevSpec, DiagID,
                                              ExplicitSpec, CloseParenLoc);
+      isFunctionSpecifier = true;
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AaronBallman wrote:

C also doesn't have `explicit`.

https://github.com/llvm/llvm-project/pull/78837