With older gcc's:

In file included from drivers/usb/class/cdc-acm.c:63:
include/linux/usb_cdc.h:117: field `bDetailData' has incomplete type
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

diff -puN include/linux/usb_cdc.h~usb_cdc-build-fix include/linux/usb_cdc.h