gallium/swr: Fix llvm11 compilation issues

Reviewed-by: Jan Zielinski <jan.zielinski@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3747>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3747>
5 files changed