Add SHA-512-256.

(Not wired up into all the signature verifiers because we don't need or
recommend that.)

Change-Id: Ia212a1f0e1c389a31d303e00a6fafb0ec3db7c71
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/40704
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/include/openssl/digest.h b/include/openssl/digest.h
index c3ceb7f..7b0ed06 100644
--- a/include/openssl/digest.h
+++ b/include/openssl/digest.h
@@ -83,6 +83,7 @@
 OPENSSL_EXPORT const EVP_MD *EVP_sha256(void);
 OPENSSL_EXPORT const EVP_MD *EVP_sha384(void);
 OPENSSL_EXPORT const EVP_MD *EVP_sha512(void);
+OPENSSL_EXPORT const EVP_MD *EVP_sha512_256(void);
 
 // EVP_md5_sha1 is a TLS-specific |EVP_MD| which computes the concatenation of
 // MD5 and SHA-1, as used in TLS 1.1 and below.