qemu cmplog+persistent mode race condition

[vanhauser-thc]

In qemu_mode (3.1.1 and 5.1), when the cmplog mode is used together with persistent mode, a race condition can happen that leads to afl-fuzz unable to communicate to that cmplog target forkserver.

The race condition only occurs in low CPU issues, e.g. in docker containers that have a --cpus=1 setting.

as a temporary workaround persistent mode is deactivated in qemu_mode 5.1, 3.11 has no workaround.