systemd-logind: Fix linking by reordering libraries in LDADD

libsystemd-audit needs functions from libsystemd-shared, so
libsystemd-audit needs to appear first.  Otherwise:

  CCLD   systemd-logind
./.libs/libsystemd-audit.a(audit.o): In function `audit_session_from_pid':
/home/josh/src/systemd/src/shared/audit.c:50: undefined reference to `detect_container'