[CMAKE] Disable unused-const-variable warning
This prevents some errors like this one:
In file included from ../dll/win32/wldap32/ber.c:27:0:
../sdk/include/reactos/wine/debug.h:378:48: error: '__wine_dbch___default' defined but not used [-Werror=unused-const-variable=]
static struct __wine_debug_channel * const __wine_dbch___default = &__wine_dbch_##ch
^
../dll/win32/wldap32/ber.c:29:1: note: in expansion of macro 'WINE_DEFAULT_DEBUG_CHANNEL'
WINE_DEFAULT_DEBUG_CHANNEL(wldap32);
^~~~~~~~~~~~~~~~~~~~~~~~~~