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

src/mips64/macro-assembler-mips64.h

Index: src/mips64/macro-assembler-mips64.h
diff --git a/src/mips64/macro-assembler-mips64.h b/src/mips64/macro-assembler-mips64.h
index a4ecae49d6a263fd47cd2e859f952ee525af0968..fa3808fa7454736de1c81c13907ff2bda77d83f0 100644
--- a/src/mips64/macro-assembler-mips64.h
+++ b/src/mips64/macro-assembler-mips64.h
@@ -22,6 +22,7 @@ const Register kInterpreterRegisterFileRegister = {Register::kCode_a7};
 const Register kInterpreterBytecodeOffsetRegister = {Register::kCode_t0};
 const Register kInterpreterBytecodeArrayRegister = {Register::kCode_t1};
 const Register kInterpreterDispatchTableRegister = {Register::kCode_t2};
+const Register kJavaScriptCallArgCountRegister = {Register::kCode_a0};
 const Register kRuntimeCallFunctionRegister = {Register::kCode_a1};
 const Register kRuntimeCallArgCountRegister = {Register::kCode_a0};