[Metadata] Use const APInt &. NFC (#101865)

getValue returns a const APInt &. So using a const APInt & will avoid a
copy.

Author: topperc

llvm/lib/IR/Metadata.cpp

@@ -1250,8 +1250,8 @@ static bool tryMergeRange(SmallVectorImpl<ConstantInt *> &EndPoints,
                           ConstantInt *Low, ConstantInt *High) {
   ConstantRange NewRange(Low->getValue(), High->getValue());
   unsigned Size = EndPoints.size();
-  APInt LB = EndPoints[Size - 2]->getValue();
-  APInt LE = EndPoints[Size - 1]->getValue();
+  const APInt &LB = EndPoints[Size - 2]->getValue();
+  const APInt &LE = EndPoints[Size - 1]->getValue();
   ConstantRange LastRange(LB, LE);
   if (canBeMerged(NewRange, LastRange)) {
     ConstantRange Union = LastRange.unionWith(NewRange);