Comment 1 for bug 1646064

The GTK+ thing definitely looks like mesa:

Thread 1 (Thread 0x7ffff7f11ac0 (LWP 13309)):
#0 rawmemchr () at ../sysdeps/x86_64/rawmemchr.S:37
#1 0x00007ffff49f9702 in _IO_str_init_static_internal (
    sf=sf@entry=0x7fffffffdef0, ptr=ptr@entry=0x0, size=size@entry=0,
    pstart=pstart@entry=0x0) at strops.c:41
#2 0x00007ffff49e6b97 in __GI___isoc99_vsscanf (string=0x0,
    format=0x7ffff30592f2 "%d.%d", args=args@entry=0x7fffffffe018)
    at isoc99_vsscanf.c:41
#3 0x00007ffff49e6b37 in __isoc99_sscanf (s=<optimized out>,
    format=<optimized out>) at isoc99_sscanf.c:31
#4 0x00007ffff303bd22 in epoxy_glx_version ()
   from /usr/lib/x86_64-linux-gnu/libepoxy.so.0
#5 0x00007ffff6b2bb49 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#6 0x00007ffff6b2befa in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#7 0x00007ffff6b34ac6 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#8 0x00007ffff6b31b36 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#9 0x00007ffff6b21a48 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0

This is deep inside the gdk_init() path.