[clang] [Clang] Add constexpr eval for cmath builtins (PR #194327)

[Hubert Tong via cfe-commits]

================
@@ -19962,10 +20032,303 @@ bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
     if (!EvaluateFloat(E->getArg(0), Result, Info) ||
         !EvaluateFloat(E->getArg(1), RHS, Info))
       return false;
+    // minimumnum handle special values (NaN, INF) per IEEE 754.
----------------
hubert-reinterpretcast wrote:

Nit:
```suggestion
    // minimumnum handles special values (NaN, INF) per IEEE 754.
```

https://github.com/llvm/llvm-project/pull/194327