support logging to syslog

don't set "log-error" on a modern system to get everything mysqld says including MDEV-20344 into a specific logfile is a dirty workaround because you spit out date/timestamp which clutters logs

MySQL supports a syslog option for years now

Aug 23 13:46:52 backupserver mysqld[489193]: 2020-08-23 13:46:52 7 [Note] Slave SQL thread exiting, replication stopped in log 'bin.000060' at position 109456465

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https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_log_syslog
[ERROR] /usr/libexec/mysqld: unknown variable 'log-syslog=1'

https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_log_error_verbosity

2020-08-16 22:17:46 0 [ERROR] /usr/libexec/mysqld: unknown variable
'log_error_verbosity=2'