[wasm] Use MachineOperatorBuilder::word() instead of kPointerSize to determine the word size.

src/compiler/int64-lowering.cc

Index: src/compiler/int64-lowering.cc
diff --git a/src/compiler/int64-lowering.cc b/src/compiler/int64-lowering.cc
index 253d2f0dc62df9f0eeb29ec744c2bd729c48336e..66122030fa06c9d1db5286848bf44e62aa2eecab 100644
--- a/src/compiler/int64-lowering.cc
+++ b/src/compiler/int64-lowering.cc
@@ -32,7 +32,7 @@ Int64Lowering::Int64Lowering(Graph* graph, MachineOperatorBuilder* machine,
 }
 
 void Int64Lowering::LowerGraph() {
-  if (4 != kPointerSize) {
+  if (machine()->word() != MachineRepresentation::kWord32) {
     return;
   }
   stack_.push(graph()->end());