pgsql: Suppress a warning that some versions of gcc emit about %x in

Log Message:
-----------
Suppress a warning that some versions of gcc emit about %x in strftime.
Per suggestion from Alvaro.

Modified Files:
--------------
pgsql/src/bin/initdb:
initdb.c (r1.137 -> r1.138)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/initdb/initdb.c.diff?r1=1.137&r2=1.138)