Fix off_t overflow in pg_basebackup on Windows.

walmethods.c used off_t to navigate around a pg_wal.tar file that could
exceed 2GB, which doesn't work on Windows and would fail with misleading
errors.  Use pgoff_t instead.

Back-patch to all supported branches.

Author: Davinder Singh <davinder.singh@enterprisedb.com>
Reported-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Discussion: https://postgr.es/m/CAKZiRmyM4YnokK6Oenw5JKwAQ3rhP0YTz2T-tiw5dAQjGRXE3Q%40mail.gmail.com

src/bin/pg_basebackup/receivelog.c

@@ -191,7 +191,7 @@ static bool
 close_walfile(StreamCtl *stream, XLogRecPtr pos)
 {
 	char	   *fn;
-	off_t		currpos;
+	pgoff_t		currpos;
 	int			r;
 	char		walfile_name[MAXPGPATH];
 

src/bin/pg_basebackup/walmethods.c

@@ -691,7 +691,7 @@ static const WalWriteMethodOps WalTarMethodOps = {
 typedef struct TarMethodFile
 {
 	Walfile		base;
-	off_t		ofs_start;		/* Where does the *header* for this file start */
+	pgoff_t		ofs_start;		/* Where does the *header* for this file start */
 	char		header[TAR_BLOCK_SIZE];
 	size_t		pad_to_size;
 } TarMethodFile;

src/bin/pg_basebackup/walmethods.h

@@ -17,7 +17,7 @@ typedef struct WalWriteMethod WalWriteMethod;
 typedef struct
 {
 	WalWriteMethod *wwmethod;
-	off_t		currpos;
+	pgoff_t		currpos;
 	char	   *pathname;
 
 	/*