Access double fields in C++ as uint64_t fields to preserve signaling bit of a NaN.

src/crankshaft/hydrogen-instructions.h

Index: src/crankshaft/hydrogen-instructions.h
diff --git a/src/crankshaft/hydrogen-instructions.h b/src/crankshaft/hydrogen-instructions.h
index 7ffb2a3a7ba10f1d03f6aa3021986cc58dd5c0c7..b2cbdab5fe108f8f6157edb241a51612b32912ca 100644
--- a/src/crankshaft/hydrogen-instructions.h
+++ b/src/crankshaft/hydrogen-instructions.h
@@ -3088,11 +3088,8 @@ class HConstant final : public HTemplateInstruction<0> {
     return double_value_;
   }
   uint64_t DoubleValueAsBits() const {
-    uint64_t bits;
     DCHECK(HasDoubleValue());
-    STATIC_ASSERT(sizeof(bits) == sizeof(double_value_));
-    std::memcpy(&bits, &double_value_, sizeof(bits));
-    return bits;
+    return bit_cast<uint64_t>(double_value_);
   }
   bool IsTheHole() const {
     if (HasDoubleValue() && DoubleValueAsBits() == kHoleNanInt64) {