Missing pthread linking flag leads to many xdemos crashing on startup

Initially stumped by glxinfo and glxgears failing to execute with error ../nptl/pthread_mutex_lock.c:424: __pthread_mutex_lock_full: Assertion 'e != ESRCH || !robust' failed. on one, and only one, of my Thinkpad T480.

After a bit of digging, turns out that -pthread needs to be among the linking flags, at least under Debian sid.

I'm happy that I've got a working glxinfo now.

From the xdemos folder, almost all applications also need this extra linking flag, i.e., glsync, glxcontexts, glxgears_fbconfig, glxgears_pixmap, glxheads, glxpbdemo, glxpixmap, glxswapcontrol, manywin, multictx, offset, overlay, pbdemo, pbinfo, shape, sharedtex, texture_from_pixmap, wincopy, xfont, and xrotfontdemo.

Update on Aug. 2nd: And the problem occurs on 3 other of my computers now, the other T480 being one of them. It's pretty clear that it was simply that the first T480 that showed the issue was ahead on the updates.