Encode alignment attribute for cmpxchg

This is a follow up patch to D83136 adding the align attribute to `cmpxchg`.
See also D83465 for `atomicrmw`.

Differential Revision: https://reviews.llvm.org/D87443

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -3060,6 +3060,7 @@ void ModuleBitcodeWriter::writeInstruction(const Instruction &I,
     Vals.push_back(
         getEncodedOrdering(cast<AtomicCmpXchgInst>(I).getFailureOrdering()));
     Vals.push_back(cast<AtomicCmpXchgInst>(I).isWeak());
+    Vals.push_back(getEncodedAlign(cast<AtomicCmpXchgInst>(I).getAlign()));
     break;
   case Instruction::AtomicRMW:
     Code = bitc::FUNC_CODE_INST_ATOMICRMW;