[clang] [Clang] restrict use of attribute names reserved by the C++ standard (PR #106036)

[Aaron Ballman via cfe-commits]

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@@ -177,6 +177,26 @@ static bool isLanguageDefinedBuiltin(const SourceManager &SourceMgr,
   return false;
 }
 
+static bool isReservedAttrName(Preprocessor &PP, IdentifierInfo *II) {
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AaronBallman wrote:

Maybe? I think they absolutely should, but those names are not portable to other compilers.

(FWIW, I like what the C committee did:

6.7.13.1p4:
> In all aspects of the language, a standard attribute specified by this document as an identifier `attr`
and an identifier of the form `__attr__` shall behave the same when used as an attribute token,
except for the spelling.

so standard library vendors can reliably use the underscored names under an existing well-known identifier reservation rule without sacrificing portability.)

https://github.com/llvm/llvm-project/pull/106036