PPC/s390: [turbofan] Introduce JSCallForwardVarargs operator.

src/s390/interface-descriptors-s390.cc

Index: src/s390/interface-descriptors-s390.cc
diff --git a/src/s390/interface-descriptors-s390.cc b/src/s390/interface-descriptors-s390.cc
index 3ffcd5fc1c1cb17e70f549bde9f6ab1354b67a03..d15bbbd5d1493dd87c0f9b45eb22890e8f16f844 100644
--- a/src/s390/interface-descriptors-s390.cc
+++ b/src/s390/interface-descriptors-s390.cc
@@ -161,6 +161,14 @@ void CallTrampolineDescriptor::InitializePlatformSpecific(
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  // r4 : start index (to support rest parameters)
+  // r3 : the target to call
+  Register registers[] = {r3, r4};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
+
 void ConstructStubDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   // r2 : number of arguments