Add two new crash commands.

One is intentionally seeting the abort message. The other is to set
the abort message to null.

Also, make the libseccomp_policy static so that the crasher
executable can be copied to the system afterwards without
requiring libseccomp_policy.so.

Test: Ran both new crash commands on device.
Test: Ran the seccomp crash command to verify seccomp still works.
Change-Id: I255b5f37e6eb188719e5b72302ca3f5911c8d821