Sort guc_parameters.dat alphabetically by name

The order in this list was previously pretty random and had grown
organically over time.  This made it unnecessarily cumbersome to
maintain these lists, as there was no clear guidelines about where to
put new entries.  Also, after the merger of the type-specific GUC
structs, the list still reflected the previous type-specific
super-order.

By using alphabetical order, the place for new entries becomes clear,
and often related entries will be listed close together.

This patch reorders the existing entries in guc_parameters.dat, and it
also augments the generation script to error if an entry is found at
the wrong place.

Note: The order is actually checked after lower-casing, to handle the
likes of "DateStyle".

Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/8fdfb91e-60fb-44fa-8df6-f5dea47353c9@eisentraut.org

src/backend/utils/misc/gen_guc_tables.pl

@@ -42,6 +42,7 @@ sub dquote
 sub print_table
 {
 	my ($ofh) = @_;
+	my $prev_name = undef;
 
 	print $ofh "\n\n";
 	print $ofh "struct config_generic ConfigureNames[] =\n";
@@ -49,6 +50,13 @@ sub print_table
 
 	foreach my $entry (@{$parse})
 	{
+		if (defined($prev_name) && lc($prev_name) ge lc($entry->{name}))
+		{
+			die sprintf(
+				"entries are not in alphabetical order: \"%s\", \"%s\"\n",
+				$prev_name, $entry->{name});
+		}
+
 		print $ofh "#ifdef $entry->{ifdef}\n" if $entry->{ifdef};
 		print $ofh "\t{\n";
 		printf $ofh "\t\t.name = %s,\n", dquote($entry->{name});
@@ -80,6 +88,8 @@ sub print_table
 		print $ofh "\t},\n";
 		print $ofh "#endif\n" if $entry->{ifdef};
 		print $ofh "\n";
+
+		$prev_name = $entry->{name};
 	}
 
 	print $ofh "\t/* End-of-list marker */\n";