libSystem not found using gfortran

[Chris Jones]

> --->  Building libgcc9
> Error: Failed to build libgcc9: command execution failed
> Error: See 
> /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_gcc9/libgcc9/main.log 
> for details.
> Error: Follow https://guide.macports.org/#project.tickets to report a bug.
> Error: Processing of port gcc9 failed
> 
> 5. The log file is 170Mb large, so I did "cat main.log | grep -i error > 
> error.log" and attach the error.log

Sorry, but I cannot tell much from that truncated log file.

Please follow the instructions to create a ticket at

ttps://guide.macports.org/#project.tickets

please also always upload complete log files from clean build attempts. 
Note, if the log is large it invariably compresses nicely with bzip2 etc. ;)

Chris