[PATCH][Bug c++/12054] Fix C++ EH bug

[Jason Merrill]

Thanks, but this is not a bug.

      15.5.1 The terminate() function           [except.terminate]
1     In the following situations exception handling must be abandoned for
           less subtle error handling techniques:
      -  when the exception handling mechanism, after completing evaluation
           of the expression to be thrown but
          before the exception is caught (15.1), calls a user function that
           exits via an uncaught exception,134)
      -  when the exception handling mechanism cannot find a handler for a
           thrown exception (15.3), or
      -  when the destruction of an object during stack unwinding (15.2)
           exits using an exception, or
      __________________
      134) For example, if the object being thrown is of a class with a
           copy constructor, terminate() will be called if that copy construc-
      tor exits with an exception during a throw.

Indeed, the cited section of the ABI document says

  (If the copy constructor itself exits by throwing an exception,
  terminate() is called.)

Jason