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

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index c240156f00386237ab99cd63fbc80772e9dd5e8a..f5f8a913e3808ba80b32ebe1baf6ad85b9c00333 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -915,6 +915,9 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
     case kArm64Int32ToFloat64:
       __ Scvtf(i.OutputDoubleRegister(), i.InputRegister32(0));
       break;
+    case kArm64Int64ToFloat32:
+      __ Scvtf(i.OutputDoubleRegister().S(), i.InputRegister64(0));
+      break;
     case kArm64Int64ToFloat64:
       __ Scvtf(i.OutputDoubleRegister(), i.InputRegister64(0));
       break;