Disable bogus GCC 7 warning about string op overflow

Analysis proves this is a false positive:

 qarraydataops.h:69:17: error: ‘void* memset(void*, int, size_t)’: specified size between 18446744056529682436 and
 18446744065119617024 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]

Change-Id: I7814054a102a407d876ffffd14b6ab0be9e222fc
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qarraydataops.h

@@ -49,6 +49,11 @@ QT_BEGIN_NAMESPACE
 
 namespace QtPrivate {
 
+QT_WARNING_PUSH
+#if defined(Q_CC_GNU) && Q_CC_GNU >= 700
+QT_WARNING_DISABLE_GCC("-Wstringop-overflow")
+#endif
+
 template <class T>
 struct QPodArrayOps
     : QTypedArrayData<T>
@@ -131,6 +136,7 @@ struct QPodArrayOps
         this->size -= (e - b);
     }
 };
+QT_WARNING_POP
 
 template <class T>
 struct QGenericArrayOps