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 9db432e5174b8dd9f871dc668485413f84f65b74..cec64badb4455e263e52f6d105b6f5ff90926956 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -656,14 +656,11 @@ enum ScopeType {
 };
 
 
-const uint32_t kHoleNanUpper32 = 0x7FFFFFFF;
-const uint32_t kHoleNanLower32 = 0xFFFFFFFF;
-const uint32_t kNaNOrInfinityLowerBoundUpper32 = 0x7FF00000;
+const uint32_t kHoleNanUpper32 = 0x7FF00000;
+const uint32_t kHoleNanLower32 = 0x7FF00000;
 
 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.