Change v4 exceptions to use the common C++ ABIs foreign exceptions

Change v4 exceptions to use the common C++ ABIs foreign exceptions

On platforms where we use the common C++ ABI, throw the exception not using a
dummy C++ exception structure and the throw keyboard, but instead use the
lower-level _Unwind_RaiseException to throw a foreign exception.  It is caught
with the existing "catch (...)" and re-throw is implemented similarly, by
grabbing the current exception from the globals (a standardized data structure)
and re-throwing it.

On platforms such as ARM that lack hooks for supplying our unwind tables to the
system run-time, this patch will make it possible to link the unwinder
statically into libQtQml (libgcc or libunwind) and thus force it to use our
unwind tables, because throwing or re-throwing will always go through our
statically linked code through direct calls to _Unwind_RaiseException (instead
of libstdc++).

Change-Id: Ic2ac056fc7ed9e93fb51e30ab45f35b260487c5f
Reviewed-by: Lars Knoll <lars.knoll@digia.com>