Provide the means to use the libc sha2 internally instead of the openssl

implementation; this does not really matter since their structs are larger
than ours, but it helps when we want to verify that we are not using any
of the openssl code.

crypto/external/bsd/openssl/dist/include/openssl/sha.h

@@ -10,6 +10,10 @@
 #ifndef HEADER_SHA_H
 # define HEADER_SHA_H
 
+#ifdef USE_LIBC_SHA2
+# include <sha2.h>
+#endif
+
 # include <openssl/e_os2.h>
 # include <stddef.h>
 
@@ -44,6 +48,7 @@ int SHA1_Final(unsigned char *md, SHA_CTX *c);
 unsigned char *SHA1(const unsigned char *d, size_t n, unsigned char *md);
 void SHA1_Transform(SHA_CTX *c, const unsigned char *data);
 
+#ifndef USE_LIBC_SHA2
 # define SHA256_CBLOCK   (SHA_LBLOCK*4)/* SHA-256 treats input data as a
                                         * contiguous array of 32 bit wide
                                         * big-endian values. */
@@ -112,6 +117,14 @@ int SHA512_Final(unsigned char *md, SHA512_CTX *c);
 unsigned char *SHA512(const unsigned char *d, size_t n, unsigned char *md);
 void SHA512_Transform(SHA512_CTX *c, const unsigned char *data);
 
+#else
+#define SHA256_CBLOCK 64
+#define SHA512_CBLOCK 128
+unsigned char *SHA256(const unsigned char *d, size_t n, unsigned char *md);
+unsigned char *SHA384(const unsigned char *d, size_t n, unsigned char *md);
+unsigned char *SHA512(const unsigned char *d, size_t n, unsigned char *md);
+#endif
+
 #ifdef  __cplusplus
 }
 #endif