Change NaN-test to only check for QNaNs, and API to only introduce QNaNs.

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index 54d7b3702da8b5404cd149c15926a4a5335e2515..b8691cae105d7cbf51e60083e46e972249d7d86b 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -1333,7 +1333,9 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) { return 0; }
 
 double OS::nan_value() {
 #ifdef _MSC_VER
-  static const __int64 nanval = 0xfff8000000000000;
+  // Positive Quiet NaN with no payload (aka. Indeterminate) has all bits
+  // in mask set, so value equals mask.
+  static const __int64 nanval = kQuietNaNMask;
   return *reinterpret_cast<const double*>(&nanval);
 #else  // _MSC_VER
   return NAN;