Add SIGHUP and SIGTERM handlers in NaCl.

Add SIGHUP and SIGTERM handlers in NaCl.

When running NaCl code in a PID namespace, we need explicit handlers for
signals that we might receive from outside the PID namespace, such as
SIGTERM. This change installs a signal handler which exits by default.

BUG= https://code.google.com/p/chromium/issues/detail?id=460972

Committed: https://chromium.googlesource.com/native_client/src/native_client/+/3b1b3cf099145cf3db831f7f29a251ac071c5290

[rickyz (no longer on Chrome), 2015-05-27 05:15:45]

rickyz@chromium.org changed reviewers:
+ jln@chromium.org, mseaborn@chromium.org

[rickyz (no longer on Chrome), 2015-05-27 05:18:48]

Hi, here's the NaCl part of the changes to enable one PID namespace per process
for NaCl processes. Init processes in PID namespaces are special in that they do
not receive signals such as SIGTERM/SIGINT unless they have an explicit handler
for these signals. This change makes NaCl manage those signals (the signal
handler exit the process with exit code -sig & 0xff by default).

[Mark Seaborn, 2015-06-04 19:44:05]

LGTM

https://codereview.chromium.org/1159803003/diff/1/src/trusted/service_runtime...
File src/trusted/service_runtime/linux/nacl_signal.c (right):

https://codereview.chromium.org/1159803003/diff/1/src/trusted/service_runtime...
src/trusted/service_runtime/linux/nacl_signal.c:46: SIGHUP, SIGINT, SIGQUIT,
SIGILL, SIGTRAP, SIGBUS, SIGFPE, SIGSEGV, SIGTERM,
Nit: your commit message says you're adding SIGINT but it's there already.

[rickyz (no longer on Chrome), 2015-06-04 22:18:50]

The CQ bit was checked by rickyz@chromium.org

[rickyz (no longer on Chrome), 2015-06-04 22:18:53]

The CQ bit was checked by rickyz@chromium.org

[commit-bot: I haz the power, 2015-06-04 22:19:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1159803003/1

[commit-bot: I haz the power, 2015-06-05 16:42:30]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/native_client/src/native_client/+/3b1b3cf09...