Reland of PPC/s390: SmiUntag only for 32bit

src/builtins/ppc/builtins-ppc.cc

Index: src/builtins/ppc/builtins-ppc.cc
diff --git a/src/builtins/ppc/builtins-ppc.cc b/src/builtins/ppc/builtins-ppc.cc
index aee21db622d32f65e6da924870add26b631116b2..5dfaa49620ca00ef156f5205858cc83fda2df501 100644
--- a/src/builtins/ppc/builtins-ppc.cc
+++ b/src/builtins/ppc/builtins-ppc.cc
@@ -2204,11 +2204,16 @@ void Builtins::Generate_CallForwardVarargs(MacroAssembler* masm,
   {
     // Load the length from the ArgumentsAdaptorFrame.
     __ LoadP(r3, MemOperand(r6, ArgumentsAdaptorFrameConstants::kLengthOffset));
+#if V8_TARGET_ARCH_PPC64
+    __ SmiUntag(r3);
+#endif
   }
   __ bind(&arguments_done);
 
   Label stack_empty, stack_done, stack_overflow;
+#if !V8_TARGET_ARCH_PPC64
   __ SmiUntag(r3);
+#endif
   __ sub(r3, r3, r5);
   __ cmpi(r3, Operand::Zero());
   __ ble(&stack_empty);