Add basic BLAKE2b-256 support.

Our use-case for this does not require optimisation at the current time,
so a clean C implementation is fine.

Change-Id: I8f29572c33e8dbcc37961c099c71c14aafc8d0a3
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/45164
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/include/openssl/base.h b/include/openssl/base.h
index b678306..90924e6 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -376,6 +376,7 @@
 typedef struct bignum_st BIGNUM;
 typedef struct bio_method_st BIO_METHOD;
 typedef struct bio_st BIO;
+typedef struct blake2b_state_st BLAKE2B_CTX;
 typedef struct bn_gencb_st BN_GENCB;
 typedef struct bn_mont_ctx_st BN_MONT_CTX;
 typedef struct buf_mem_st BUF_MEM;