Make use of sigchainlib for signal chaining for implicit checks

This adds a preload library that overrides sigaction and sigprocmask
to implement signal chaining.  Signal chaining allows us to chain
any signal so that the ART runtime receives it before any signal
handler registered in native code by an application.  If the
ART signal handler doesn't want it, it will pass it on to the
user's handler.

ART uses signals for null pointer checks, stack overflow checks and
suspend points.

Also adds an OAT test to test this in isolation.

Change-Id: I9545f9f7343774c091410eb810504d9855fd399f