Follows 107d3d461f and other 'pthread->std::thread' diffs.
Windows uses Structured Exception Handling to allow reporting errors
(both C++ and hardware) nicely. This works by wrapping the code in a
__try __catch block.
The pthread wrapper did this automatically, but we now need to do it
explicitly for std::thread.
Tested by: Stan
Differential Revision: https://code.wildfiregames.com/D3261
This was SVN commit r24530.
