[RegisterConfiguration] Streamline access to arch defaults, simplify Registers.

test/cctest/compiler/test-multiple-return.cc

Index: test/cctest/compiler/test-multiple-return.cc
diff --git a/test/cctest/compiler/test-multiple-return.cc b/test/cctest/compiler/test-multiple-return.cc
index 53bae5e0f37a6012964b2cef4417d1ee51cfee96..aa7ec02a6695d28121130363d729acfb121fe51c 100644
--- a/test/cctest/compiler/test-multiple-return.cc
+++ b/test/cctest/compiler/test-multiple-return.cc
@@ -27,8 +27,7 @@ CallDescriptor* GetCallDescriptor(Zone* zone, int return_count,
                                   int param_count) {
   MachineSignature::Builder msig(zone, return_count, param_count);
   LocationSignature::Builder locations(zone, return_count, param_count);
-  const RegisterConfiguration* config =
-      RegisterConfiguration::ArchDefault(RegisterConfiguration::TURBOFAN);
+  const RegisterConfiguration* config = RegisterConfiguration::Turbofan();
 
   // Add return location(s).
   CHECK(return_count <= config->num_allocatable_general_registers());