Comment 2 for bug 1696353

The problem with doing that is that it doesn't actually change the behaviour. We use pthread_create to create the new thread, which glibc does with a clone with CLONE_SYSVSEM set. We can't tell the difference between "guest program needs the new threads to not share SysV semaphore behaviour" and "guest program doesn't care but didn't provide the flag" so we err on the side of caution and refuse to create a thread that doesn't behave the way the guest asked us for it to behave.