errno code is no longer OS specific. Moving to common.

This fix uses the fmt::safe_strerror instead of the underlying
strerror_r functionality. I think this is better - but I'm not
sure if there is a reason for avoiding the use of this function.

Failure to compile to systems that don't have a valid definition
of strerror_r.

Support for AIX. Tested on AIX 6.1 with GCC 6.3.

Added file header support for step_logger

Update step_logger