pgsql: Oops, add proper #ifdef for systems without support for syslog.

Log Message:
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Oops, add proper #ifdef for systems without support for syslog.

Per buildfarm member mastodon.

Modified Files:
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pgsql/src/backend/utils/misc:
guc.c (r1.442 -> r1.443)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.442&r2=1.443)