Fix pg_verify_checksums on Windows.

To verify the checksums, we open the file in text mode which doesn't work
on Windows as WIN32 treats Control-Z as EOF in files opened in text mode.
This leads to "short read of block .." error in some cases.

Fix it by opening the files in the binary mode.

Author: Amit Kapila
Reviewed-by: Magnus Hagander
Backpatch-through: 11
Discussion: https://postgr.es/m/CAA4eK1+LOnzod+h85FGmyjWzXKy-XV1FYwEyP-Tky2WpD5cxwA@mail.gmail.com

src/bin/pg_verify_checksums/pg_verify_checksums.c

@@ -83,7 +83,7 @@ scan_file(char *fn, int segmentno)
 	int			f;
 	int			blockno;
 
-	f = open(fn, 0);
+	f = open(fn, O_RDONLY | PG_BINARY);
 	if (f < 0)
 	{
 		fprintf(stderr, _("%s: could not open file \"%s\": %s\n"),