Sync our copy of the timezone library with IANA release tzcode2018g.

This patch absorbs an upstream fix to "zic" for a recently-introduced
bug that made it output data that some 32-bit clients couldn't read.
Given the current source data, the bug only manifests in zones with
leap seconds, which we don't generate, so that there's no actual
change in our installed timezone data files from this.  Still, in
case somebody uses our copy of "zic" to do something else, it seems
best to apply the fix promptly.

Also, update the README's notes about converting upstream code to
our conventions.

src/timezone/README

@@ -55,7 +55,7 @@ match properly on the old version.
 Time Zone code
 ==============
 
-The code in this directory is currently synced with tzcode release 2018f.
+The code in this directory is currently synced with tzcode release 2018g.
 There are many cosmetic (and not so cosmetic) differences from the
 original tzcode library, but diffs in the upstream version should usually
 be propagated to our version.  Here are some notes about that.
@@ -73,13 +73,18 @@ fixed that.)
 includes relying on configure's results rather than hand-hacked #defines,
 and not relying on <stdint.h> features that may not exist on old systems.
 (In particular this means using Postgres' definitions of the int32 and
-int64 typedefs, not int_fast32_t/int_fast64_t.)
+int64 typedefs, not int_fast32_t/int_fast64_t.  Likewise we use
+PG_INT32_MIN/MAX not INT32_MIN/MAX.)
 
 * Since Postgres is typically built on a system that has its own copy
 of the <time.h> functions, we must avoid conflicting with those.  This
 mandates renaming typedef time_t to pg_time_t, and similarly for most
 other exposed names.
 
+* zic.c's typedef "lineno" is renamed to "lineno_t", because having
+"lineno" in our typedefs list would cause unfortunate pgindent behavior
+in some other files where we have variables named that.
+
 * We have exposed the tzload() and tzparse() internal functions, and
 slightly modified the API of the former, in part because it now relies
 on our own pg_open_tzfile() rather than opening files for itself.
@@ -108,8 +113,11 @@ to first run the tzcode source files through a sed filter like this:
         -e 's/\bregister[ \t]//g' \
         -e 's/int_fast32_t/int32/g' \
         -e 's/int_fast64_t/int64/g' \
+        -e 's/INT32_MIN/PG_INT32_MIN/g' \
+        -e 's/INT32_MAX/PG_INT32_MAX/g' \
         -e 's/struct[ \t]+tm\b/struct pg_tm/g' \
         -e 's/\btime_t\b/pg_time_t/g' \
+        -e 's/lineno/lineno_t/g' \
 
 and then run them through pgindent.  (The first three sed patterns deal
 with conversion of their block comment style to something pgindent

src/timezone/zic.c

@@ -167,9 +167,11 @@ PERCENT_Z_LEN_BOUND = sizeof "+995959" - 1};
    QTBUG-53071 <https://bugreports.qt.io/browse/QTBUG-53071>.  This
    workaround will no longer be needed when Qt 5.6.1 and earlier are
    obsolete, say in the year 2021.  */
+#ifndef WORK_AROUND_QTBUG_53071
 enum
 {
 WORK_AROUND_QTBUG_53071 = true};
+#endif
 
 static int	charcnt;
 static bool errors;
@@ -1912,12 +1914,6 @@ atcomp(const void *avp, const void *bvp)
 	return (a < b) ? -1 : (a > b);
 }
 
-static bool
-is32(const zic_t x)
-{
-	return x == ((zic_t) ((int32) x));
-}
-
 static void
 swaptypes(int i, int j)
 {
@@ -1971,7 +1967,12 @@ writezone(const char *const name, const char *const string, char version,
 	zic_t		one = 1;
 	zic_t		y2038_boundary = one << 31;
 	ptrdiff_t	nats = timecnt + WORK_AROUND_QTBUG_53071;
-	zic_t	   *ats = emalloc(size_product(nats, sizeof *ats + 1));
+
+	/*
+	 * Allocate the ATS and TYPES arrays via a single malloc, as this is a bit
+	 * faster.
+	 */
+	zic_t	   *ats = emalloc(MAXALIGN(size_product(nats, sizeof *ats + 1)));
 	void	   *typesptr = ats + nats;
 	unsigned char *types = typesptr;
 
@@ -2029,20 +2030,6 @@ writezone(const char *const name, const char *const string, char version,
 		types[i] = attypes[i].type;
 	}
 
-	/*
-	 * Work around QTBUG-53071 for timestamps less than y2038_boundary - 1, by
-	 * inserting a no-op transition at time y2038_boundary - 1. This works
-	 * only for timestamps before the boundary, which should be good enough in
-	 * practice as QTBUG-53071 should be long-dead by 2038.
-	 */
-	if (WORK_AROUND_QTBUG_53071 && timecnt != 0
-		&& ats[timecnt - 1] < y2038_boundary - 1 && strchr(string, '<'))
-	{
-		ats[timecnt] = y2038_boundary - 1;
-		types[timecnt] = types[timecnt - 1];
-		timecnt++;
-	}
-
 	/*
 	 * Correct for leap seconds.
 	 */
@@ -2057,6 +2044,23 @@ writezone(const char *const name, const char *const string, char version,
 			}
 	}
 
+	/*
+	 * Work around QTBUG-53071 for timestamps less than y2038_boundary - 1, by
+	 * inserting a no-op transition at time y2038_boundary - 1. This works
+	 * only for timestamps before the boundary, which should be good enough in
+	 * practice as QTBUG-53071 should be long-dead by 2038.  Do this after
+	 * correcting for leap seconds, as the idea is to insert a transition just
+	 * before 32-bit pg_time_t rolls around, and this occurs at a slightly
+	 * different moment if transitions are leap-second corrected.
+	 */
+	if (WORK_AROUND_QTBUG_53071 && timecnt != 0
+		&& ats[timecnt - 1] < y2038_boundary - 1 && strchr(string, '<'))
+	{
+		ats[timecnt] = y2038_boundary - 1;
+		types[timecnt] = types[timecnt - 1];
+		timecnt++;
+	}
+
 	/*
 	 * Figure out 32-bit-limited starts and counts.
 	 */
@@ -2064,25 +2068,24 @@ writezone(const char *const name, const char *const string, char version,
 	timei32 = 0;
 	leapcnt32 = leapcnt;
 	leapi32 = 0;
-	while (timecnt32 > 0 && !is32(ats[timecnt32 - 1]))
+	while (0 < timecnt32 && PG_INT32_MAX < ats[timecnt32 - 1])
 		--timecnt32;
-	while (timecnt32 > 0 && !is32(ats[timei32]))
+	while (1 < timecnt32 && ats[timei32] < PG_INT32_MIN
+		   && ats[timei32 + 1] <= PG_INT32_MIN)
 	{
+		/*
+		 * Discard too-low transitions, except keep any last too-low
+		 * transition if no transition is exactly at PG_INT32_MIN. The kept
+		 * transition will be output as an PG_INT32_MIN "transition"
+		 * appropriate for buggy 32-bit clients that do not use time type 0
+		 * for timestamps before the first transition; see below.
+		 */
 		--timecnt32;
 		++timei32;
 	}
-
-	/*
-	 * Output an INT32_MIN "transition" if appropriate; see below.
-	 */
-	if (timei32 > 0 && ats[timei32] > PG_INT32_MIN)
-	{
-		--timei32;
-		++timecnt32;
-	}
-	while (leapcnt32 > 0 && !is32(trans[leapcnt32 - 1]))
+	while (0 < leapcnt32 && PG_INT32_MAX < trans[leapcnt32 - 1])
 		--leapcnt32;
-	while (leapcnt32 > 0 && !is32(trans[leapi32]))
+	while (0 < leapcnt32 && trans[leapi32] < PG_INT32_MIN)
 	{
 		--leapcnt32;
 		++leapi32;
@@ -2315,7 +2318,8 @@ writezone(const char *const name, const char *const string, char version,
 			if (pass == 1)
 
 				/*
-				 * Output an INT32_MIN "transition" if appropriate; see above.
+				 * Output an PG_INT32_MIN "transition" if appropriate; see
+				 * above.
 				 */
 				puttzcode(((ats[i] < PG_INT32_MIN) ?
 						   PG_INT32_MIN : ats[i]), fp);