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 11613d14027d9c6195516492d9e7eed5a7a2d458..7a2d6595f3f9d0e98ce24dfa26ce9180a29602c1 100644
--- a/src/arm/interface-descriptors-arm.cc
+++ b/src/arm/interface-descriptors-arm.cc
@@ -393,6 +393,21 @@ void ApiAccessorDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   data->Initialize(arraysize(registers), registers, representations,
                    &default_descriptor);
 }
+
+
+void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      cp,  // context
+      r1,  // math rounding function
+      r3,  // vector slot id
+  };
+  Representation representations[] = {
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+  };
+  data->Initialize(arraysize(registers), registers, representations);
+}
 }
 }  // namespace v8::internal