Add server client certificate support for TLS v1.2 . This is more complex

than client side as we need to keep the handshake record cache frozen when
it contains all the records need to process the certificate verify message.
(backport from HEAD).

ssl/ssl_locl.h

@@ -1092,4 +1092,5 @@ int ssl_parse_clienthello_renegotiate_ext(SSL *s, unsigned char *d, int len,
 					  int *al);
 long ssl_get_algorithm2(SSL *s);
 int tls1_process_sigalgs(SSL *s, const unsigned char *data, int dsize);
+int tls12_get_req_sig_algs(SSL *s, unsigned char *p);
 #endif