jackaudio: use ifdefs to hide unavailable functions

jackaudio: use ifdefs to hide unavailable functions

On Windows the jack_set_thread_creator() function and on MacOS the
pthread_setname_np() function with a thread pointer paramater is
not available. Use #ifdefs to remove the jack_set_thread_creator()
function call and the qjack_thread_creator() function in both
cases.

The qjack_thread_creator() function just sets the name of the
created thread for debugging purposes and isn't really necessary.

From the jack_set_thread_creator() documentation:
(...)

No normal application/client should consider calling this. (...)

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/785
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20211226154017.6067-1-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>