Add a new convenience macro for an exception handler that handles all exceptions.

Add a new convenience macro for an exception handler that handles all exceptions.

When using native compiler exceptions, the previous method of doing
this, __EXCEPT(NULL), would expand to __except(
(NULL)(GetExceptionInformation())) which doesn't compile as NULL isn't a
function.

So add a new macro, __EXCEPT_ALL, which works correctly both when using
native compiler exceptions and without and which makes the meaning of
code in which it is used clearer.