automake: require shared glapi when using DRI based libGL

This has been a requirement for ages, yet it seems like we never
explicitly errored out during configure.

CC: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit a7ea7511)