[turbofan] Implement the call protocol properly for direct calls.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 45b792f9dbda80b0775db0c1be623833e050d1da..1d1ae4ec2a353e6dfe805d99ad760a48a9d3d125 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -25,6 +25,7 @@ const Register kInterpreterRegisterFileRegister = {Register::kCode_r11};
 const Register kInterpreterBytecodeOffsetRegister = {Register::kCode_r12};
 const Register kInterpreterBytecodeArrayRegister = {Register::kCode_r14};
 const Register kInterpreterDispatchTableRegister = {Register::kCode_r15};
+const Register kJavaScriptCallArgCountRegister = {Register::kCode_rax};
 const Register kRuntimeCallFunctionRegister = {Register::kCode_rbx};
 const Register kRuntimeCallArgCountRegister = {Register::kCode_rax};