CHROMIUM: x86: add HAVE_SECCOMP_FILTER and seccomp_execve

CHROMIUM: x86: add HAVE_SECCOMP_FILTER and seccomp_execve

BugLink: http://bugs.launchpad.net/bugs/887780

Adds support to the x86 architecture by providing a compatibility
mode wrapper for sys_execve's number and selecting HAVE_SECCOMP_FILTER

v9: rebase on to bccaeafd7c117acee36e90d37c7e05c19be9e7bf

Signed-off-by: Will Drewry <wad@chromium.org>
BUG=chromium-os:14496
TEST=see others ref'd in bug

Change-Id: Id0e8440181e98f7edb12ef702f2f6bdca54d15a6
Reviewed-on: http://gerrit.chromium.org/gerrit/3244
Reviewed-by: Sonny Rao <sonnyrao@chromium.org>
Tested-by: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <kees.cook@canonical.com>