Fix some BufFileRead() error reporting

Remove "%m" from error messages where errno would be bogus.  Add short
read byte counts where appropriate.

This is equivalent to what was done in
7897e3b, but some code was apparently
developed concurrently to that and not updated accordingly.

Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/f3501945-c591-8cc3-5ef0-b72a2e0eaa9c@enterprisedb.com

src/backend/replication/backup_manifest.c

@@ -358,7 +358,8 @@ SendBackupManifest(backup_manifest_info *manifest)
 		if (rc != bytes_to_read)
 			ereport(ERROR,
 					(errcode_for_file_access(),
-					 errmsg("could not read from temporary file: %m")));
+					 errmsg("could not read from temporary file: read only %zu of %zu bytes",
+							rc, bytes_to_read)));
 		pq_putmessage('d', manifestbuf, bytes_to_read);
 		manifest_bytes_done += bytes_to_read;
 	}