SECCOMP bpf backport

Seccomp bpf (also called filter/mode 2) backport
Has some ARM-specific code from git.chromium.org/gitweb/?p=chromiumos/third_party/kernel.git, the rest comes from https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tag/?id=v3.8

This is necessary for the upcoming sandboxing support in FirefoxOS.

See also https://bugzilla.mozilla.org/show_bug.cgi?id=790923