[CIR][NFC] Fix CIR build after CharUnits change (llvm#161580)

My previous attempt to fix this missed one case.

Author: andykaylor

clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp

@@ -824,7 +824,7 @@ void CIRRecordLowering::lowerUnion() {
     appendPaddingBytes(layoutSize - getSize(storageType));
 
   // Set packed if we need it.
-  if (layoutSize % getAlignment(storageType))
+  if (!layoutSize.isMultipleOf(getAlignment(storageType)))
     packed = true;
 }