[turbofan] Add operators for float32 support.

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index bac15768270f4fe0808c31332e261dac81312dce..ae87dc4d31b01763eef756a1058a05ca0dc1561e 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -67,6 +67,14 @@ inline unsigned int FastD2UI(double x) {
 }
 
 
+inline float DoubleToFloat32(double x) {
+  // TODO(yanggou): This static_cast is implementation-defined behaviour in C++,
+  // so we may need to do the conversion manually instead to match the spec.
+  volatile float f = static_cast<float>(x);
+  return f;
+}
+
+
 inline double DoubleToInteger(double x) {
   if (std::isnan(x)) return 0;
   if (!std::isfinite(x) || x == 0) return x;