Fix SetThreadName on Linux

[norihiro]

Description

SetThreadName set the name of current thread, where it is expected to set the target thread. This change will store the name if the thread is not started. Then, set the name after the thread is created.

The original code uses prctl to set the name. However, the cast to unsigned long will loose the upper 32-bit of the 64-bit pointer on 64-bit system. This PR also fix to use pthread_setname_np to fix the issue.

ntv2/ajalibraries/ajabase/system/linux/threadimpl.cpp

Line 612 in 2e64749

int ret = prctl(PR_SET_NAME, (unsigned long)name, 0, 0);

Step to reproduce the issue

OS: Fedora Linux 34

1. Start OBS Studio with AJA
2. Start AJA Output on OBS Studio
3. Run top

Without this fix, top shows AJA Video Outpu as the name of the main thread of OBS Studio.
With this fix, top shows the original name of the thread. When hit H, still AJA Video Outpu appears as another thread.