PPC/s390: [turbofan] Introduce JSCallForwardVarargs operator.

src/ppc/interface-descriptors-ppc.cc

Index: src/ppc/interface-descriptors-ppc.cc
diff --git a/src/ppc/interface-descriptors-ppc.cc b/src/ppc/interface-descriptors-ppc.cc
index 4ff59bbaf1087da8ef2dc260ca2a9097a532ce05..75a5a0a695cac58e766e364574829ecfc6ef2c7f 100644
--- a/src/ppc/interface-descriptors-ppc.cc
+++ b/src/ppc/interface-descriptors-ppc.cc
@@ -174,6 +174,13 @@ void CallTrampolineDescriptor::InitializePlatformSpecific(
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  // r5 : start index (to support rest parameters)
+  // r4 : the target to call
+  Register registers[] = {r4, r5};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
 
 void ConstructStubDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {