Try to handle exceptions coming from the JIT.

The idea is whenever there is an exception cling to be able to recover from it
and continue working. For example:
[cling] throw 12;
shouldn't crash the current session in the interpreter. Now that we have compiled
the UserInterface with exceptions on, I hoped to be able to catch exceptions
coming from the JIT easily, but obviously I am still missing something.
The standard said use catch(...) and not catch()
Move the handling of unhandled exceptions in the loop.

Indeed if the UserInterface.cpp is compiled without -fno-exceptions I get:
****************** CLING ******************
* Type C++ code and press enter to run it *
*             Type .q to exit             *
*******************************************
[cling]$ throw 12;
Exception occurred. Recovering...
[cling]$ .q

So the issue is still in the build system, because I built UserInterface.cpp 'by hand'.