Booting without loading any extensions, I get this with tc-17.x x86_64: tce-load -i Xorg-7.7 flwm aterm wbar
startx..and the gui starts.
I get this in /var/log/Xorg.0.log: [ 34.827] (EE) Failed to load /usr/local/lib/xorg/modules/extensions/libglx.so: libGL.so.1: cannot open shared object file: No such file or directory
...
[ 34.829] (EE) Failed to load /usr/local/lib/xorg/modules/drivers/modesetting_drv.so: libgbm.so.1: cannot open shared object file: No such file or directory..but the gui still works
Edit: I get the same thing with tc-17.x x86, except that the system hangs on exit to prompt.
In addition, I cannot use the modesetting driver with x86 otherwise the system hangs, I'm obliged to use the obsolete xf86-video-intel extension, whereas both work with x86_64.