seccomp: Enable speculation flaw mitigations

seccomp: Enable speculation flaw mitigations

When speculation flaw mitigations are opt-in (via prctl), using seccomp
will automatically opt-in to these protections, since using seccomp
indicates at least some level of sandboxing is desired.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
CVE-2018-3639 (x86)

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>