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

src/crankshaft/x87/lithium-codegen-x87.cc

Index: src/crankshaft/x87/lithium-codegen-x87.cc
diff --git a/src/crankshaft/x87/lithium-codegen-x87.cc b/src/crankshaft/x87/lithium-codegen-x87.cc
index dee8cdf804b69da61b77d84a34596d1fa2c93df0..740812e5fc2ef788a5f4c32fa550384ffe1b3a40 100644
--- a/src/crankshaft/x87/lithium-codegen-x87.cc
+++ b/src/crankshaft/x87/lithium-codegen-x87.cc
@@ -3724,7 +3724,9 @@ void LCodeGen::PrepareForTailCall(const ParameterCount& actual,
 #endif
   if (FLAG_code_comments) {
     if (actual.is_reg()) {
-      Comment(";;; PrepareForTailCall, actual: %s {", actual.reg().ToString());
+      Comment(";;; PrepareForTailCall, actual: %s {",
+              RegisterConfiguration::Crankshaft()->GetGeneralRegisterName(
+                  actual.reg().code()));
     } else {
       Comment(";;; PrepareForTailCall, actual: %d {", actual.immediate());
     }