log uncaught C++ exceptions in main
log uncaught C++ exceptions in main

Summary:
Uncaught C++ exceptions on Windows aren't logged in a very helpful
way. Print a more useful message to the log.

Reviewed By: wez

Differential Revision: D21671280

fbshipit-source-id: f450ed7bcd2ccabf999ea0eae5ed18442f80a3a3

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