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.

OraBug: 28041771
CVE: CVE-2018-3639

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit 5c3070890d06ff82eecb808d02d2ca39169533ef)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
 Conflicts:
	kernel/seccomp.c
[The include file is called nospec-branch.h instead of nospec.h]

Signed-off-by: Brian Maly <brian.maly@oracle.com>