Fix assertion failure in PR98681 (llvm#98860)

See https://en.cppreference.com/w/cpp/numeric/math/pow:
```
C++98 added overloads where exp has type int on top of C [pow()](https://en.cppreference.com/w/c/numeric/math/pow), and the return type of std::pow(float, int) was float. However, the additional overloads introduced in C++11 specify that std::pow(float, int) should return double. [LWG issue 550](https://cplusplus.github.io/LWG/issue550) was raised to target this conflict, and the resolution is to removed the extra int exp overloads.
```

Author: dtcxzyw

llvm/lib/Analysis/ConstantFolding.cpp

@@ -2759,7 +2759,7 @@ static Constant *ConstantFoldIntrinsicCall2(Intrinsic::ID IntrinsicID, Type *Ty,
         switch (Ty->getTypeID()) {
         case Type::HalfTyID:
         case Type::FloatTyID: {
-          APFloat Res(std::pow(Op1V.convertToFloat(), Exp));
+          APFloat Res(static_cast<float>(std::pow(Op1V.convertToFloat(), Exp)));
           if (Ty->isHalfTy()) {
             bool Unused;
             Res.convert(APFloat::IEEEhalf(), APFloat::rmNearestTiesToEven,

llvm/test/Transforms/EarlyCSE/math-2.ll

@@ -108,4 +108,12 @@ define half @pr98665() {
   ret half %x
 }
 
+define float @powi_f32() {
+; CHECK-LABEL: @powi_f32(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %y = call float @llvm.powi.f32.i32(float 0.0, i32 10)
+  ret float %y
+}
+
 attributes #0 = { nofree nounwind willreturn }