r300: fail linking instead of using dummy shaders

r300: fail linking instead of using dummy shaders

We need to tell the apps about the hardware limtations, so that they
have a chance to take a fallback path. Fixes GTK misrendering, due to
use of the dummy shaders (now properly fallbacks to software).

Based on a MR by Filip Gawin.

Closes:https://gitlab.freedesktop.org/mesa/mesa/-/issues/7291

Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Reviewed-by: Filip Gawin <filip.gawin@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22708>