tweak try_and_catch test for windows
tweak try_and_catch test for windows

Summary: Tweak a test that relies on hardcoding the expected result of `std::exception().what()` instead to call that and use the result without hardcoding it.

Differential Revision: D26573226

fbshipit-source-id: 3802d12186c96b864e2680d99f5cfca185235f8d

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly