Summary

Fix a build and behavior issue in log.c where vsyslog() is conditionally compiled using an incorrect macro: HAVE_VSYSLOG_H.

Problem

The current code checks for vsyslog() support using:

#ifdef HAVE_VSYSLOG_H
    vsyslog(level, fmt, args);

However, vsyslog.h does not exist in any standard C library. Since vsyslog() is not part of the POSIX standard, it should be detected using Autoconf via AC_CHECK_FUNCS, rather than relying on a non-existent header macro.

Fix

• In configure.ac, modified the function checks from:

  AC_CHECK_FUNCS([strlcpy strlcat setgroups])

  to:

  AC_CHECK_FUNCS([strlcpy strlcat setgroups vsyslog])

• In log.c, updated the conditional compilation to:

  #ifdef HAVE_VSYSLOG
      vsyslog(level, fmt, args);