[LibCallsShrinkWrap] Avoid use of ConstantExpr::getFPExtend() (NFC)

Use the constant folding API instead.

Author: nikic

llvm/lib/Transforms/Utils/LibCallsShrinkWrap.cpp

@@ -101,7 +101,7 @@ class LibCallsShrinkWrap : public InstVisitor<LibCallsShrinkWrap> {
                     float Val) {
     Constant *V = ConstantFP::get(BBBuilder.getContext(), APFloat(Val));
     if (!Arg->getType()->isFloatTy())
-      V = ConstantExpr::getFPExtend(V, Arg->getType());
+      V = ConstantFoldCastInstruction(Instruction::FPExt, V, Arg->getType());
     if (BBBuilder.GetInsertBlock()->getParent()->hasFnAttribute(Attribute::StrictFP))
       BBBuilder.setIsFPConstrained(true);
     return BBBuilder.CreateFCmp(Cmp, Arg, V);