Also dump a stack trace on a pthread assertion failure

Also dump a stack trace on a pthread assertion failure

Recently on the build bots we hit a pthread_error (https://build.chromium.org/p/client.dart/builders/vm-linux-debug-x64-reload-be/builds/337/steps/vm%20tests/logs/stdio)
 but that code uses a different ASSERT macro so we don't get to see the stack trace.

BUG=
R=fschneider@google.com

Committed: https://github.com/dart-lang/sdk/commit/a7fe93b62cfb77b02540dd95ef661c5cd8b44f6b

[Cutch, 2016-09-27 18:04:31]

Description was changed from

==========
Also dump a stack trace on a pthread assertion failure

BUG=
==========

to

==========
Also dump a stack trace on a pthread assertion failure

Recently on the build bots we hit a pthread_error
(https://build.chromium.org/p/client.dart/builders/vm-linux-debug-x64-reload-b...)
 but that code uses a different ASSERT macro so we don't get to see the stack
trace.

BUG=
==========

[Cutch, 2016-09-27 18:04:31]

johnmccutchan@google.com changed reviewers:
+ fschneider@google.com, rmacnak@google.com

[Florian Schneider, 2016-09-27 18:15:33]

lgtm

[Cutch, 2016-09-27 18:16:33]

Description was changed from

==========
Also dump a stack trace on a pthread assertion failure

Recently on the build bots we hit a pthread_error
(https://build.chromium.org/p/client.dart/builders/vm-linux-debug-x64-reload-b...)
 but that code uses a different ASSERT macro so we don't get to see the stack
trace.

BUG=
==========

to

==========
Also dump a stack trace on a pthread assertion failure

Recently on the build bots we hit a pthread_error
(https://build.chromium.org/p/client.dart/builders/vm-linux-debug-x64-reload-b...)
 but that code uses a different ASSERT macro so we don't get to see the stack
trace.

BUG=
R=fschneider@google.com

Committed:
https://github.com/dart-lang/sdk/commit/a7fe93b62cfb77b02540dd95ef661c5cd8b44f6b
==========

[Cutch, 2016-09-27 18:16:35]

Committed patchset #1 (id:1) manually as
a7fe93b62cfb77b02540dd95ef661c5cd8b44f6b (presubmit successful).

[rmacnak, 2016-09-27 18:18:40]

Stack dumps are already printed for FATALs. I suspect there's no trace for that
run because a second crash occurred attempting to create the trace.