Avoid unportable strftime() behavior in pg_dump/pg_dumpall.

Commit ad5d46a4494b0b480a3af246bb4227d9bdadca37 thought that we could
get around the known portability issues of strftime's %Z specifier by
using %z instead.  However, that idea seems to have been innocent of
any actual research, as it certainly missed the facts that
(1) %z is not portable to pre-C99 systems, and
(2) %z doesn't actually act differently from %Z on Windows anyway.

Per failures on buildfarm member hamerkop.

While at it, centralize the code defining what strftime format we
want to use in pg_dump; three copies of that string seems a bit much.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/bin/pg_dump/pg_backup_archiver.c b/src/bin/pg_dump/pg_backup_archiver.c
index ed28d36e138..1a2ebcb1f48 100644
--- a/src/bin/pg_dump/pg_backup_archiver.c
+++ b/src/bin/pg_dump/pg_backup_archiver.c
@@ -1047,14 +1047,16 @@ PrintTOCSummary(Archive *AHX, RestoreOptions *ropt)
 	teSection	curSection;
 	OutputContext sav;
 	const char *fmtName;
-	struct tm  *tm = localtime(&AH->createDate);
 	char		stamp_str[64];
 
 	sav = SaveOutput(AH);
 	if (ropt->filename)
 		SetOutput(AH, ropt->filename, 0 /* no compression */ );
 
-	strftime(stamp_str, sizeof(stamp_str), "%Y-%m-%d %H:%M:%S %z", tm);
+	if (strftime(stamp_str, sizeof(stamp_str), PGDUMP_STRFTIME_FMT,
+				 localtime(&AH->createDate)) == 0)
+		strcpy(stamp_str, "[unknown]");
+
 	ahprintf(AH, ";\n; Archive created at %s\n", stamp_str);
 	ahprintf(AH, ";     dbname: %s\n;     TOC Entries: %d\n;     Compression: %d\n",
 			 AH->archdbname, AH->tocCount, AH->compression);
@@ -3544,7 +3546,7 @@ dumpTimestamp(ArchiveHandle *AH, const char *msg, time_t tim)
 {
 	char		buf[64];
 
-	if (strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %z", localtime(&tim)) != 0)
+	if (strftime(buf, sizeof(buf), PGDUMP_STRFTIME_FMT, localtime(&tim)) != 0)
 		ahprintf(AH, "-- %s %s\n\n", msg, buf);
 }