Install the "posixrules" timezone link in MSVC builds.

Somehow, we'd missed ever doing this.  The consequences aren't too
severe: basically, the timezone library would fall back on its hardwired
notion of the DST transition dates to use for a POSIX-style zone name,
rather than obeying US/Eastern which is the intended behavior.  The net
effect would only be to obey current US DST law further back than it
ought to apply; so it's not real surprising that nobody noticed.

David Rowley, per report from Amit Kapila

Discussion: https://postgr.es/m/CAA4eK1LC7CaNhRAQ__C3ht1JVrPzaAXXhEJRnR5L6bfYHiLmWw@mail.gmail.com

src/tools/msvc/Install.pm

@@ -380,13 +380,20 @@ sub GenerateTimezoneFiles
 	my $conf   = shift;
 	my $mf     = read_file("src/timezone/Makefile");
 	$mf =~ s{\\\r?\n}{}g;
+
 	$mf =~ /^TZDATA\s*:?=\s*(.*)$/m
 	  || die "Could not find TZDATA line in timezone makefile\n";
 	my @tzfiles = split /\s+/, $1;
 
+	$mf =~ /^POSIXRULES\s*:?=\s*(.*)$/m
+	  || die "Could not find POSIXRULES line in timezone makefile\n";
+	my $posixrules = $1;
+	$posixrules =~ s/\s+//g;
+
 	print "Generating timezone files...";
 
-	my @args = ("$conf/zic/zic", '-d', "$target/share/timezone");
+	my @args = ("$conf/zic/zic", '-d', "$target/share/timezone",
+				'-p', "$posixrules");
 	foreach (@tzfiles)
 	{
 		my $tzfile = $_;