[clang] [Clang] Add __datasizeof (PR #67805)

[Aaron Ballman via cfe-commits]

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@@ -236,6 +236,7 @@ FEATURE(shadow_call_stack,
 FEATURE(tls, PP.getTargetInfo().isTLSSupported())
 FEATURE(underlying_type, LangOpts.CPlusPlus)
 FEATURE(experimental_library, LangOpts.ExperimentalLibrary)
+FEATURE(datasizeof, LangOpts.CPlusPlus)
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AaronBallman wrote:

Oh my. That behavior makes sense, but is really not helpful in this case.

You could use compiler version macro checks instead of `__has_extension`. That's pretty gross and likely easy to forget, but would it be a viable workaround?

https://github.com/llvm/llvm-project/pull/67805