X87: Add a MathFloor stub generated with TurboFan

src/x87/interface-descriptors-x87.cc

Index: src/x87/interface-descriptors-x87.cc
diff --git a/src/x87/interface-descriptors-x87.cc b/src/x87/interface-descriptors-x87.cc
index 515d56c659d2db936f868c91ef4641c93f8311f2..c9c277542831dbd324aae7af6c901b4db55c74dd 100644
--- a/src/x87/interface-descriptors-x87.cc
+++ b/src/x87/interface-descriptors-x87.cc
@@ -370,6 +370,21 @@ void ApiAccessorDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   };
   data->Initialize(arraysize(registers), registers, representations);
 }
+
+
+void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      esi,  // context
+      edi,  // math rounding function
+      edx,  // vector slot id
+  };
+  Representation representations[] = {
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+  };
+  data->Initialize(arraysize(registers), registers, representations);
+}
 }
 }  // namespace v8::internal