Use signaling NaN for holes in fixed double arrays.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 4b9f79b9e8b09afc6169930f2caded85a1650076..7180b811499dbd3355d92f7d510a5ea076f61a5d 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -657,14 +657,11 @@ enum ScopeType {
 };
 
 
-const uint32_t kHoleNanUpper32 = 0x7FFFFFFF;
-const uint32_t kHoleNanLower32 = 0xFFFFFFFF;
-const uint32_t kNaNOrInfinityLowerBoundUpper32 = 0x7FF00000;
+const uint32_t kHoleNanUpper32 = 0xFFF7FFFF;
+const uint32_t kHoleNanLower32 = 0xFFF7FFFF;
 
 const uint64_t kHoleNanInt64 =
     (static_cast<uint64_t>(kHoleNanUpper32) << 32) | kHoleNanLower32;
-const uint64_t kLastNonNaNInt64 =
-    (static_cast<uint64_t>(kNaNOrInfinityLowerBoundUpper32) << 32);
 
 
 // The order of this enum has to be kept in sync with the predicates below.