Fedora 42 is going to use gcc 15 which uses the C23 standard. This converted a number of warnings into errors. I've addressed the errors in https://github.com/cyrusimap/cyrus-sasl/pull/869
The issues addressed include:
- The RETURN macro is defined differently in two places. Rename one.
- Both atexit and the sigint and sigterm actions call server_exit().
The function arguments diff. Introduce a new generic signal handler to
call server_exit() for sigint and sigterm signals.
