Add a MathFloor stub generated with TurboFan

src/arm/interface-descriptors-arm.cc

Index: src/arm/interface-descriptors-arm.cc
diff --git a/src/arm/interface-descriptors-arm.cc b/src/arm/interface-descriptors-arm.cc
index caff56d5c85a4d4f4098503d4534b9fb1cd6f601..ed2bc38e08fb174ccc577cff87f7234c6484b89d 100644
--- a/src/arm/interface-descriptors-arm.cc
+++ b/src/arm/interface-descriptors-arm.cc
@@ -387,6 +387,21 @@ void ApiAccessorDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   data->Initialize(arraysize(registers), registers, representations,
                    &default_descriptor);
 }
+
+
+void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      r1,  // context
+      r2,  // math rounding function
+      r3,  // vector slot id
+  };
+  Representation representations[] = {
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+  };
+  data->Initialize(arraysize(registers), registers, representations);
+}
 }
 }  // namespace v8::internal