treewide: Allow additional system calls for i386/i686

I haven't tested i386 for a long time (after playing with some
openSUSE i586 image a couple of years ago). It turns out that a number
of system calls we actually need were denied by the seccomp filter,
and not even basic functionality works.

Add some system calls that glibc started using with the 64-bit time
("t64") transition, see also:

  https://wiki.debian.org/ReleaseGoals/64bit-time

that is: clock_gettime64, timerfd_gettime64, fcntl64, and
recvmmsg_time64.

Add further system calls that are needed regardless of time_t width,
that is, mmap2 (valgrind profile only), _llseek and sigreturn (common
outside x86_64), and socketcall (same as s390x).

I validated this against an almost full run of the test suite, with
just a few selected tests skipped. Fixes needed to run most tests on
i386/i686, and other assorted fixes for tests, are included in
upcoming patches.

Reported-by: Uroš Knupleš <uros@knuples.net>
Analysed-by: Faidon Liambotis <paravoid@debian.org>
Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1078981
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

passt.c

@@ -191,11 +191,11 @@ void exit_handler(int signal)
  * Return: non-zero on failure
  *
  * #syscalls read write writev
- * #syscalls socket bind connect getsockopt setsockopt s390x:socketcall close
- * #syscalls recvfrom sendto shutdown
+ * #syscalls socket getsockopt setsockopt s390x:socketcall i686:socketcall close
+ * #syscalls bind connect recvfrom sendto shutdown
  * #syscalls arm:recv ppc64le:recv arm:send ppc64le:send
  * #syscalls accept4|accept listen epoll_ctl epoll_wait|epoll_pwait epoll_pwait
- * #syscalls clock_gettime arm:clock_gettime64
+ * #syscalls clock_gettime arm:clock_gettime64 i686:clock_gettime64
  */
 int main(int argc, char **argv)
 {