Switch to the new kernel API for obtaining fault address tag bits.

The discussion on LKML is converging on v16 of the fault address tag
bits patch [1]. In this version of the patch the presence of the tag
bits in si_addr is controlled by a sa_flags bit, and a protocol is
introduced to allow userspace to detect kernel support for sa_flags
bits. Update the tombstone signal handler to use this API to read
the tag bits, update the interceptors in libsigchain to implement
the flag support detection protocol and hide the tag bits in si_addr
from chained signal handlers that did not request them to match the
kernel behavior.

[1] https://lore.kernel.org/linux-arm-kernel/cover.1605235762.git.pcc@google.com/

Change-Id: I57f24c07c01ceb3e5b81cfc15edf559ef7dfc740