Implemented the RoundInt64ToFloat32 TurboFan operator for x64, arm64, and mips64.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index e77b005ea2a0d41b085b4413f3d166c0e708194f..631c10d1242909536cdc449b51cc31a011454a09 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -930,6 +930,12 @@ void InstructionSelector::VisitTruncateInt64ToInt32(Node* node) {
 }
 
 
+void InstructionSelector::VisitRoundInt64ToFloat32(Node* node) {
+  X64OperandGenerator g(this);
+  Emit(kSSEInt64ToFloat32, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
+}
+
+
 void InstructionSelector::VisitRoundInt64ToFloat64(Node* node) {
   X64OperandGenerator g(this);
   Emit(kSSEInt64ToFloat64, g.DefineAsRegister(node), g.Use(node->InputAt(0)));