turn off /EHa

Summary:
The /EHa flag tells MSVC to catch asynchronous (structured) exceptions
in `catch(...)` blocks. This is generally a bad idea, because
structured exceptions include page faults, stack overflow, division by
zero, and illegal instructions, at which point attempting to run
further arbitrary C++ code will have wonky effects in the best
case. It would probably also clobber any state required to debug the
original failure.

Reviewed By: Orvid

Differential Revision: D16390933

fbshipit-source-id: 2997daaf350680dc9d0c7da3cabab8749e8ecb82

CMake/FollyCompilerMSVC.cmake

@@ -80,7 +80,7 @@ function(apply_folly_compile_options_to_target THETARGET)
   # The general options passed:
   target_compile_options(${THETARGET}
     PUBLIC
-      /EHa # Enable both SEH and C++ Exceptions.
+      /EHs # Don't catch structured exceptions with catch (...)
       /GF # There are bugs with constexpr StringPiece when string pooling is disabled.
       /Zc:referenceBinding # Disallow temporaries from binding to non-const lvalue references.
       /Zc:rvalueCast # Enforce the standard rules for explicit type conversion.