This works around a spurious gcc warning:

../wine/dlls/win32u/message.c: In function ‘unpack_message.constprop’:
../wine/dlls/win32u/message.c:359:9: error: writing 28 bytes into a region of size 4 [-Werror=stringop-overflow=]
  359 |         memcpy( &ps->wp, &wp, sizeof(wp) );
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../wine/dlls/win32u/win32u_private.h:29,
                 from ../wine/dlls/win32u/message.c:30:
../wine/include/ntuser.h:549:15: note: destination object ‘hwnd’ of size 4
  549 |     UINT      hwnd;
      |               ^~~~