termios breakage on LM32

[Sebastien Bourdeauducq]

This has to do with changes in the interrupt API and a buggy update of
the handler code (cpukit/score/cpu/lm32/irq.c) that caused various
problems (stack corruption, etc.)

I have copied the NIOS code and added _exception_stack_frame the best I
could; it works much better now but it could still use some
understanding and testing.
https://github.com/milkymist/rtems/commit/e0d4d55f693886b991c1b35b53091d005cea8cf5

S.