Thanks a lot. This was very helpful. I was able to build mesa-21.3.8 on debian testing.
I still have two problems though.
Some applications (alacritty, for example) break because of xinput2. alacritty throws up following error:
thread 'main' panicked at 'X server has XInput extension 1.3 but does not support XInput2', /home/vikas/.cargo/registry/src/github.com-1ecc6299db9ec823/winit-0.26.1/src/platform_impl/linux/x11/mod.rs:176:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
My browser (qutebrowser) throws the warning about Xinput2 but starts. But it refuses to work because it says "network change detected". If I reload the page multiple times, some of the pages load. But the browser is unusable. I do not have the same problem with firefox. I understand that this is more likely to be a problem with qutebrowser. And is not likely to be related to the original issue of this thread (glx, that is).
But if anyone on the list has a similar experience and a solution, I will be grateful.
Vikas