PPC: [runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

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 48adcf3fab58af961e48f5469320e27219f704a6..70dcb0fffa2529818f2c92866970610bd5026c47 100644
--- a/src/ppc/interface-descriptors-ppc.cc
+++ b/src/ppc/interface-descriptors-ppc.cc
@@ -99,6 +99,10 @@ void ToNumberDescriptor::InitializePlatformSpecific(
 
 
 // static
+const Register ToStringDescriptor::ReceiverRegister() { return r3; }
+
+
+// static
 const Register ToObjectDescriptor::ReceiverRegister() { return r3; }