score: Rename _Internal_error_Occurred()

Rename _Internal_error_Occurred() into _Terminate().
score: _Thread_Start_multitasking()

Fix serious race-condition.  Read the heir after the per-CPU lock
acquire.
score: _CPU_SMP_Get_current_processor()

Remove RTEMS_COMPILER_PURE_ATTRIBUTE from _SMP_Get_current_processor()
and all _CPU_SMP_Get_current_processor().  Make inline ASM statements
volatile again.  Test smptests/smpmigration01 showed that GCC optimizes
too much otherwise.
bsp/score603e: Remove unused BSP_fatal_return()
bsps/sparc: Delete unused file
bsp/leon3: Add leon3_power_down_loop()
bsp/leon3: Add and use leon3_get_cpu_count()
bsp/leon3: Add bsp_reset() for SMP configuration