mac: handle low-level errors

- update low-level hmac functions from macros to functions.
- libgcrypt: propagate low-level hmac errors.
- libgcrypt: add error checks for hmac calls.
- os400qc3: add error checks, propagate them.
  Assisted-by: Patrick Monnerat
- mbedtls: fix propagating low-level hmac errors.
- wincng: fix propagating low-level hmac errors.
- mac: verify success of low-level hmac functions.
- knownhost: verify success of low-level hmac functions.
- transport: verify success of MAC hash call.
- minor type cleanup in wincng.
- delete unused ripemd wrapper in wincng.
- delete unused SHA384 wrapper in mbedtls.

Reported-by: Paul Howarth
Reviewed-by: Michael Buckley
Closes #1297

include/libssh2.h

@@ -587,6 +587,7 @@ typedef struct _LIBSSH2_POLLFD {
 #define LIBSSH2_ERROR_RANDGEN                   -49
 #define LIBSSH2_ERROR_MISSING_USERAUTH_BANNER   -50
 #define LIBSSH2_ERROR_ALGO_UNSUPPORTED          -51
+#define LIBSSH2_ERROR_MAC_FAILURE               -52
 
 /* this is a define to provide the old (<= 1.2.7) name */
 #define LIBSSH2_ERROR_BANNER_NONE LIBSSH2_ERROR_BANNER_RECV