lorder: process read-only data symbols

Previously they were skipped. lorder(1) serves no functional purpose
today but we might as well address this longstanding bug while it is
still in the tree.

PR: 133860
MFC after: 1 week
Submitted by: John Hein

(cherry picked from commit e1d6d6f9249d37c10a0df68024c7dacebdc7bf98)