Clang: ExprConstant use maxnum/minnum for fmax/fmin

In APFloat, we have defined maxnum and minnum, so let's use them
directly here.

Author: wzssyqa

clang/lib/AST/ExprConstant.cpp

@@ -15604,16 +15604,11 @@ bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
   case Builtin::BI__builtin_fmaxl:
   case Builtin::BI__builtin_fmaxf16:
   case Builtin::BI__builtin_fmaxf128: {
-    // TODO: Handle sNaN.
     APFloat RHS(0.);
     if (!EvaluateFloat(E->getArg(0), Result, Info) ||
         !EvaluateFloat(E->getArg(1), RHS, Info))
       return false;
-    // When comparing zeroes, return +0.0 if one of the zeroes is positive.
-    if (Result.isZero() && RHS.isZero() && Result.isNegative())
-      Result = RHS;
-    else if (Result.isNaN() || RHS > Result)
-      Result = RHS;
+    Result = maxnum(Result, RHS);
     return true;
   }
 
@@ -15622,16 +15617,11 @@ bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
   case Builtin::BI__builtin_fminl:
   case Builtin::BI__builtin_fminf16:
   case Builtin::BI__builtin_fminf128: {
-    // TODO: Handle sNaN.
     APFloat RHS(0.);
     if (!EvaluateFloat(E->getArg(0), Result, Info) ||
         !EvaluateFloat(E->getArg(1), RHS, Info))
       return false;
-    // When comparing zeroes, return -0.0 if one of the zeroes is negative.
-    if (Result.isZero() && RHS.isZero() && RHS.isNegative())
-      Result = RHS;
-    else if (Result.isNaN() || RHS < Result)
-      Result = RHS;
+    Result = minnum(Result, RHS);
     return true;
   }