that structure is undefined because that source file includes
<linux/compat.h>, which turns around and includes <asm/compat.h>
which, for i386, doesn't exist:
$ find include -name compat.h
include/asm-ia64/compat.h
include/config/video/v4l1/compat.h
include/config/sonypi/compat.h
include/asm-s390/compat.h
include/asm-mips/compat.h
include/linux/compat.h
include/asm-parisc/compat.h
include/asm-sparc64/compat.h
include/asm-x86_64/compat.h
include/asm-powerpc/compat.h
include/net/compat.h
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA
http://crashcourse.ca
========================================================================
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