[turbofan] Make MachineType a pair of enums.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index 1175027f924b9422041a27c7c0b1515b77058cd5..801c97aa7c684efd2130c973f51a94b17ec1495a 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -105,7 +105,7 @@ class PipelineData {
     source_positions_.Reset(new SourcePositionTable(graph_));
     simplified_ = new (graph_zone_) SimplifiedOperatorBuilder(graph_zone_);
     machine_ = new (graph_zone_) MachineOperatorBuilder(
-        graph_zone_, kMachPtr,
+        graph_zone_, MachineType::PointerRepresentation(),
         InstructionSelector::SupportedMachineOperatorFlags());
     common_ = new (graph_zone_) CommonOperatorBuilder(graph_zone_);
     javascript_ = new (graph_zone_) JSOperatorBuilder(graph_zone_);