Use xorps xmm1, xmm1 to creat a 0.0 cconstant. Add to utils a bitwise double test.

runtime/platform/utils.h

Index: runtime/platform/utils.h
===================================================================
--- runtime/platform/utils.h	(revision 35714)
+++ runtime/platform/utils.h	(working copy)
@@ -179,6 +179,10 @@
   static uint16_t HostToLittleEndian16(uint16_t host_value);
   static uint32_t HostToLittleEndian32(uint32_t host_value);
   static uint64_t HostToLittleEndian64(uint64_t host_value);
+
+  static bool DoublesBitEqual(const double a, const double b) {
+    return bit_cast<int64_t, double>(a) == bit_cast<int64_t, double>(b);
+  }
 };
 
 }  // namespace dart