[clang] [C++23] [CLANG] Adding C++23 constexpr math functions: fmin and frexp. (PR #88978)

[Hubert Tong via cfe-commits]

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@@ -3440,7 +3440,7 @@ def Fmod : FPMathTemplate, LibBuiltin<"math.h"> {
 
 def Frexp : FPMathTemplate, LibBuiltin<"math.h"> {
   let Spellings = ["frexp"];
-  let Attributes = [NoThrow];
+  let Attributes = [NoThrow, Constexpr];
   let Prototype = "T(T, int*)";
   let AddBuiltinPrefixedAlias = 1;
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hubert-reinterpretcast wrote:

Should probably match `Fmin` on this:
```suggestion
  let AddBuiltinPrefixedAlias = 1;
  let OnlyBuiltinPrefixedAliasIsConstexpr = 1;
```

https://github.com/llvm/llvm-project/pull/88978