Silence a GCC 8 warning in QIODevice

qtbase/src/corelib/io/qiodevice.cpp:688:60:   required from here
../../../include/QtCore/../../../../qtbase/src/corelib/tools/qvector.h:727:20: error: ‘void* memmove(void*, const void*, size_t)’ writing to an object of type ‘class QRingBuffer’ with no trivial copy-assignment; use copy-assignment or copy-initialization instead [-Werror=class-memaccess]
             memmove(i, b, (d->size - offset) * sizeof(T));
             ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Change-Id: I9dc9a17c281b71bf2eb3e89116600ec3ba345d74
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/corelib/tools/qvector.h

@@ -724,7 +724,7 @@ typename QVector<T>::iterator QVector<T>::insert(iterator before, size_type n, c
         } else {
             T *b = d->begin() + offset;
             T *i = b + n;
-            memmove(i, b, (d->size - offset) * sizeof(T));
+            memmove(static_cast<void *>(i), static_cast<const void *>(b), (d->size - offset) * sizeof(T));
             while (i != b)
                 new (--i) T(copy);
         }