build: fix 'make dist' error

build: fix 'make dist' error

When I run 'make dist', I receive the following error messages:
make[1]: Entering directory `/home/wency/source/libvirt/src'
  GEN    remote/remote_protocol.h
  GEN    remote/remote_protocol.c
  GEN    remote/qemu_protocol.h
  GEN    remote/qemu_protocol.c
  GEN    remote/qemu_client_bodies.h
  CC     libvirt_driver_remote_la-remote_protocol.lo
In file included from ./remote/remote_protocol.h:16,
                 from ./remote/remote_protocol.c:7:
/internal.h:249:23: error: probes.h: No such file or directory
make[1]: *** [libvirt_driver_remote_la-remote_protocol.lo] Error 1
make[1]: Leaving directory `/home/wency/source/libvirt/src'
make: *** [distdir] Error 1

The reason is that we use probes.h before generating it.