Force the TZ environment variable to be set during initdb. This is to

short-circuit the rather expensive identify_system_timezone() procedure,
which we have no real need for during initdb since nothing done here depends
on the timezone setting.  Since we launch quite a few standalone backends
during the initdb sequence, this adds up to a significant savings, and seems
worth doing to save developer time even though it will hardly matter to end
users.  Per my report today on pgsql-hackers.

src/bin/initdb/initdb.c

@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  * Portions taken from FreeBSD.
  *
- * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.178 2009/12/11 03:34:56 itagaki Exp $
+ * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.179 2009/12/18 18:45:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2712,6 +2712,14 @@ main(int argc, char *argv[])
 	sprintf(pgdenv, "PGDATA=%s", pg_data);
 	putenv(pgdenv);
 
+	/*
+	 * Also ensure that TZ is set, so that we don't waste time identifying the
+	 * system timezone each of the many times we start a standalone backend.
+	 * It's okay to use a hard-wired value here because nothing done during
+	 * initdb cares about the timezone setting.
+	 */
+	putenv("TZ=GMT");
+
 	if ((ret = find_other_exec(argv[0], "postgres", PG_BACKEND_VERSIONSTR,
 							   backend_exec)) < 0)
 	{