gallium/auxiliary: Fix uses of gnu struct = {} extension

gallium/auxiliary: Fix uses of gnu struct = {} extension

Most of these will never actually be compiled by windows, but in the
interest of being able to make using struct foo = {}; an error and
avoiding breaking windows removing a handful of safe uses seems like a
good trade off.

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Acked-by: Eric Engestrom <eric.engestrom@intel.com>