This change includes support for a variant of [HRSS], a post-quantum KEM
based on NTRU. It includes changes suggested in [SXY]. This is not yet
ready for any deployment: some breaking changes, like removing the
confirmation hash, are still planned.
(CLA for HRSS's assembly code noted in b/119426559.)
[HRSS] https://eprint.iacr.org/2017/667.pdf
[SXY] https://eprint.iacr.org/2017/1005.pdf
Change-Id: I85d813733b066d5c578484bdd248de3f764194db
Reviewed-on: https://boringssl-review.googlesource.com/c/33105
Reviewed-by: David Benjamin <davidben@google.com>
