Add a MathFloor stub generated with TurboFan

src/x64/interface-descriptors-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/interface-descriptors.h"
 
@@ skipping 353 matching lines @@
   };
   Representation representations[] = {
       Representation::Tagged(),    // context
       Representation::Tagged(),    // callee
       Representation::Tagged(),    // call_data
       Representation::Tagged(),    // holder
       Representation::External(),  // api_function_address
   };
   data->Initialize(arraysize(registers), registers, representations);
 }
+
+
+void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      rsi,  // context
+      rdi,  // math rounding function
+      rdx,  // vector slot id
+  };
+  Representation representations[] = {
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+  };
+  data->Initialize(arraysize(registers), registers, representations);
+}
 }
 }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64