The setup code uses octal values with printf to generate a BOM for
UTF-16/32 BE/LE. It specifically uses '\777' to emit a 0xff byte. This
relies on the fact that most shells truncate the value above 0o377.
Ash however interprets '\777' as '\77' + a literal '7', resulting in an
invalid BOM.
Fix this by using the proper value of 0xff: '\377'.
Signed-off-by: Kevin Daudt <me@ikke.info> Signed-off-by: Junio C Hamano <gitster@pobox.com>