Add Semaphore and its test, and use it where semaphores are needed

Add Semaphore and its test, and use it where semaphores are needed.

TEST=util_test Semaphore.*:ProcessReader.*:ExceptionPorts.*
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/b7a10703359ab6b409c5d031e97a96df9301117a

[Mark Mentovai, 2014-09-22 23:12:12]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Mark Mentovai, 2014-09-23 00:46:55]

You can hold off on this, because I want to rethink it. I might want to get rid
of the semaphores altogether and just go with mutexes
(base/synchronization/lock). Do you have any thoughts on that?

[Mark Mentovai, 2014-09-23 04:05:21]

I looked at this more closely and found that it’s really not easily workable
with mutexes (base/synchronization/lock), and it’s sold me even more on using
semaphores as they’re used here. I’d like to proceed with this.

[Robert Sesek, 2014-09-24 16:18:15]

LGTM. Yes, the primitives in base/ are not useful for creating a semaphore.

[Mark Mentovai, 2014-09-24 17:32:36]

Committed patchset #1 (id:1) manually as b7a10703359a (presubmit successful).