[ConstantFolding] Avoid use of ConstantExpr::getOr() (NFC)

Constant folding cannot fail here, because we're really working
on plain integers. It might be better to make all of this work
on APInts instead of Constants.

llvm/lib/Analysis/ConstantFolding.cpp

@@ -235,7 +235,8 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
         ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize;
 
         // Mix it in.
-        Elt = ConstantExpr::getOr(Elt, Src);
+        Elt = ConstantFoldBinaryOpOperands(Instruction::Or, Elt, Src, DL);
+        assert(Elt && "Constant folding cannot fail on plain integers");
       }
       Result.push_back(Elt);
     }