Skip setting seccomp filter when running with ASan.

Also add an example build target for an ASan-ified libminijail (useful
for debugging).

Bug: 28052772
Bug: 27980137

(cherry picked from commit 2413f3713ae8a306a23550e2eecd59f380f34eae)

Change-Id: I0b07b17934221a7ff4bd0b58641e4e7afb225aa6
3 files changed