Reland: Add unoptimized/optimized variants of MathFloor TF code stub

src/x64/interface-descriptors-x64.cc

Index: src/x64/interface-descriptors-x64.cc
diff --git a/src/x64/interface-descriptors-x64.cc b/src/x64/interface-descriptors-x64.cc
index 7602403508739cdcce27f420bda349b3ec32f742..4f43569c35caca2ddbbbeaaaba70e7bc2e226325 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -332,11 +332,22 @@ void ApiAccessorDescriptor::InitializePlatformSpecific(
 }
 
 
-void MathRoundVariantDescriptor::InitializePlatformSpecific(
-    CallInterfaceDescriptorData* data) {
+void MathRoundVariantCallFromUnoptimizedCodeDescriptor::
+    InitializePlatformSpecific(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      rdi,  // math rounding function
+      rdx,  // vector slot id
+  };
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
+
+
+void MathRoundVariantCallFromOptimizedCodeDescriptor::
+    InitializePlatformSpecific(CallInterfaceDescriptorData* data) {
   Register registers[] = {
       rdi,  // math rounding function
       rdx,  // vector slot id
+      rbx   // type vector
   };
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }