From: Arnd Bergmann <arnd@arndb.de>

I have tested the code with the open posix test suite and found the same
four failures for both 64-bit and compat mode, most tests pass.  The patch
is against -mc1, but I guess it also applies to the other trees around.

What worries me more than mq_attr compatibility is the conversion of struct
sigevent, which might turn out really hard when more fields in there are
used.  AFAICS, the only other part in the kernel ABI is sys_timer_create(),
so maybe it's not too late to deprecate the current structure and create a
structure that can be used properly for compat syscalls.