[turbofan] Add an InterpreterDispatch linkage type.

src/compiler/linkage.h

Index: src/compiler/linkage.h
diff --git a/src/compiler/linkage.h b/src/compiler/linkage.h
index 31b9faca2a9f15f145141b2160c117b6c24fb3cd..45d15c9eead52a5cdc709f20b4c19fc4261accbf 100644
--- a/src/compiler/linkage.h
+++ b/src/compiler/linkage.h
@@ -63,9 +63,10 @@ class CallDescriptor final : public ZoneObject {
  public:
   // Describes the kind of this call, which determines the target.
   enum Kind {
-    kCallCodeObject,  // target is a Code object
-    kCallJSFunction,  // target is a JSFunction object
-    kCallAddress      // target is a machine pointer
+    kCallCodeObject,      // target is a Code object
+    kCallJSFunction,      // target is a JSFunction object
+    kCallAddress,         // target is a machine pointer
+    kInterpreterDispatch  // target is an interpreter bytecode handler
   };
 
   enum Flag {
@@ -111,6 +112,8 @@ class CallDescriptor final : public ZoneObject {
   // Returns {true} if this descriptor is a call to a JSFunction.
   bool IsJSFunctionCall() const { return kind_ == kCallJSFunction; }
 
+  bool IsInterpreterDispatch() const { return kind_ == kInterpreterDispatch; }
+
   // The number of return values from this call.
   size_t ReturnCount() const { return machine_sig_->return_count(); }
 
@@ -235,6 +238,12 @@ class Linkage : public ZoneObject {
   static CallDescriptor* GetSimplifiedCDescriptor(Zone* zone,
                                                   const MachineSignature* sig);
 
+  // Creates a call descriptor for interpreter handler code stubs. These are not
+  // intended to be called directly but are instead dispatched to by the
+  // interpreter.
+  static CallDescriptor* GetInterpreterDispatchDescriptor(
+      Zone* zone, const MachineSignature* sig);
+
   // Get the location of an (incoming) parameter to this function.
   LinkageLocation GetParameterLocation(int index) const {
     return incoming_->GetInputLocation(index + 1);  // + 1 to skip target.