On Alpine, SDL is built with directfb support and this triggers warnings
during QEMU build
In file included from /usr/include/directfb/direct/thread.h:38,
from /usr/include/directfb/direct/debug.h:43,
from /usr/include/directfb/direct/interface.h:36,
from /usr/include/directfb/directfb.h:49,
from /usr/include/SDL2/SDL_syswm.h:80,
from /builds/berrange/qemu/include/ui/sdl2.h:8,
from ../ui/sdl2-gl.c:31:
/usr/include/directfb/direct/os/waitqueue.h:41:25: error: redundant
redeclaration of 'direct_waitqueue_init' [-Werror=redundant-decls]
41 | DirectResult DIRECT_API direct_waitqueue_init ( DirectWaitQueue
*queue );
| ^~~~~~~~~~~~~~~~~~~~~