perror(1): Replace magic exit codes with standard macros

Signed-off-by: Faraz Vahedi <kfv@kfv.io>
Reviewed by: markj, oshogbo
MFC after: 1 week
Pull Request: https://github.com/freebsd/freebsd-src/pull/1492

(cherry picked from commit 4dd6597a56f8c7ff03d4f451b612a9e45442c549)