* cpu_asm.S: Added support for the debug exception vector, cleaned
up the exception processing & exception return stuff. Re-added
EPC in the task context structure so the gdb stub will know where
a thread is executing. Should've left it there in the first place...
* idtcpu.h: Added support for the debug exception vector.
* cpu.c: Added ___exceptionTaskStack to hold a pointer to the
stack frame in an interrupt so context switch code can get the
userspace EPC when scheduling.
* rtems/score/cpu.h: Re-added EPC to the task context.
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