[turbofan] Combine family of CallRuntime() methods into single imeplementation.

src/code-factory.h

Index: src/code-factory.h
diff --git a/src/code-factory.h b/src/code-factory.h
index 8171ef76414b4dc6ac85eea76dc297c78308e700..fd85ee1fb741dd378961c24f00578c904d67a403 100644
--- a/src/code-factory.h
+++ b/src/code-factory.h
@@ -30,6 +30,8 @@ class Callable final BASE_EMBEDDED {
 
 class V8_EXPORT_PRIVATE CodeFactory final {
  public:
+  static Handle<Code> RuntimeCEntry(Isolate* isolate, int result_size = 1);

[Michael Starzinger, 2016/12/15 14:39:58]

Can we leave a comment here explaining that the {CEntryStub} has var-args
semantics ("argv" is passed on the stack and "argc" is passed via a register),
to explain the asymmetry why there is no CallInterfaceDescriptor available for
this "RuntimeCEntry" code.

+
   // Initial states for ICs.
   static Callable LoadIC(Isolate* isolate);
   static Callable LoadICInOptimizedCode(Isolate* isolate);