[turbofan] Use CompareNilIC for abstract equality with null/undefined.

src/full-codegen/ppc/full-codegen-ppc.cc

Index: src/full-codegen/ppc/full-codegen-ppc.cc
diff --git a/src/full-codegen/ppc/full-codegen-ppc.cc b/src/full-codegen/ppc/full-codegen-ppc.cc
index ad401de848efdba14cde58432a43e7e33c663ccf..ff210fc628e43ef2279fd7c8ee7d1dff0a42af75 100644
--- a/src/full-codegen/ppc/full-codegen-ppc.cc
+++ b/src/full-codegen/ppc/full-codegen-ppc.cc
@@ -4957,8 +4957,8 @@ void FullCodeGenerator::EmitLiteralCompareNil(CompareOperation* expr,
   } else {
     Handle<Code> ic = CompareNilICStub::GetUninitialized(isolate(), nil);
     CallIC(ic, expr->CompareOperationFeedbackId());
-    __ cmpi(r3, Operand::Zero());
-    Split(ne, if_true, if_false, fall_through);
+    __ CompareRoot(r3, Heap::kTrueValueRootIndex);
+    Split(eq, if_true, if_false, fall_through);
   }
   context()->Plug(if_true, if_false);
 }