(In reply to comment #17)
> Can I just stop gdm set the environment and start gdm with systemctl?

I don't think so. It mainly needs to be in gnome-shell's environment, but I'm
not sure offhand how best to achieve that with your setup.

>     --with-gallium-drivers=r300,r600,radeonsi,nouveau,svga,swrast \

You only need r600 and maybe swrast here.

>     --with-dri-drivers=i915,i965,r200,radeon,nouveau,swrast \

You can set this to an empty string.

>     --enable-egl \
>     --enable-gallium-egl \
>     --with-egl-platforms=x11,drm \

Shouldn't need these.

>     --enable-gbm \

Shouldn't need this.

>     --enable-osmesa \

Don't need this.

>     --enable-gles1 \
>     --enable-gles2 \

Shouldn't need these.

>     --enable-xa \
>     --enable-vdpau "

Don't need these.