[clang] [clang][C23] Allow NaN in constant evaluation (PR #167892)

[Aaron Ballman via cfe-commits]

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@@ -222,6 +222,8 @@ C23 Feature Support
   the same translation unit but from different types.
 - ``-MG`` now silences the "file not found" errors with ``#embed`` when
   scanning for dependencies and encountering an unknown file. #GH165632
+- Allow NaN in constant expression evaluation to maintain consistency with
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AaronBallman wrote:

Is that a challenge though? I guess I see that as the status quo with the current runtime behavior, at least for floating-point types. Implementations that follow IEEE define the behavior for their users, and implementations which don't follow IEEE may or may not define the behavior. That's conditional support, effectively.

https://github.com/llvm/llvm-project/pull/167892