remove horrible pragma macro and remove __owur from SSL_CTX_add_session() declaration

Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4014)

include/openssl/ssl.h

@@ -1559,7 +1559,7 @@ int SSL_SESSION_up_ref(SSL_SESSION *ses);
 void SSL_SESSION_free(SSL_SESSION *ses);
 __owur int i2d_SSL_SESSION(SSL_SESSION *in, unsigned char **pp);
 __owur int SSL_set_session(SSL *to, SSL_SESSION *session);
-__owur int SSL_CTX_add_session(SSL_CTX *s, SSL_SESSION *c);
+int SSL_CTX_add_session(SSL_CTX *s, SSL_SESSION *c);
 int SSL_CTX_remove_session(SSL_CTX *, SSL_SESSION *c);
 __owur int SSL_CTX_set_generate_session_id(SSL_CTX *, GEN_SESSION_CB);
 __owur int SSL_set_generate_session_id(SSL *, GEN_SESSION_CB);

ssl/ssl_sess.c

@@ -549,10 +549,7 @@ int ssl_get_prev_session(SSL *s, CLIENTHELLO_MSG *hello, int *al)
                  * interrupt the session resumption process. The return
                  * value is intentionally ignored.
                  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wunused-result"
                 SSL_CTX_add_session(s->session_ctx, ret);
-#pragma GCC diagnostic pop
             }
         }
     }