MSVC 2013 build has been broken

Building TOT with MSVC2013 gives the error:

```
(ClCompile target) -> 
  C:\pbrt-v3\src\ext\glog\src\logging.cc(1154): error C2483: 'thread_msg_data' : object with constructor or destructor cannot be declared 'thread' [c:\pbrt-v3\build\src\ext\glog\glog.vcxproj]
```

It looks like this is due to the changes introduced in 2df0ca34aa3000dadf76633ca700abf0bf50756d.