Copy or check ShortData rather than pointer in more places

This follows-up on commit 4d24fcd3e1 -
when ShortData is bigger than a pointer (on 32-bit systems, when using
64-bit ShortData), copying d isn't sufficient; data must be copied.
Likewise, comparing d to check for equality is insufficient when
isShort(), as the other may also be short and differ in the more
significant bytes.

Change-Id: I49c0cf33727b8b43436cf0e3f57f602e83226885
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/time/qdatetime.cpp

@@ -3016,7 +3016,7 @@ inline QDateTime::Data::Data(Qt::TimeSpec spec)
 }
 
 inline QDateTime::Data::Data(const Data &other) noexcept
-    : d(other.d)
+    : data(other.data)
 {
     if (!isShort()) {
         // check if we could shrink
@@ -3033,17 +3033,17 @@ inline QDateTime::Data::Data(const Data &other) noexcept
 }
 
 inline QDateTime::Data::Data(Data &&other) noexcept
-    : d(other.d)
+    : data(other.data)
 {
     // reset the other to a short state
     Data dummy;
     Q_ASSERT(dummy.isShort());
-    other.d = dummy.d;
+    other.data = dummy.data;
 }
 
 inline QDateTime::Data &QDateTime::Data::operator=(const Data &other) noexcept
 {
-    if (d == other.d)
+    if (isShort() ? data == other.data : d == other.d)
         return *this;
 
     auto x = d;

src/corelib/time/qdatetime.h

@@ -266,6 +266,8 @@ class Q_CORE_EXPORT QDateTime
 #if Q_BYTE_ORDER == Q_BIG_ENDIAN
         quintptr status : 8;
 #endif
+        friend constexpr bool operator==(const ShortData &lhs, const ShortData &rhs)
+        { return lhs.status == rhs.status && lhs.msecs == rhs.msecs; }
     };
 
     union Data {