Fixes the type of global variable _sys_idle_elapsed_ticks such that
both its nanokernel and microkernel definitions are of the same
type--int32_t.
One of the repercussions of this is that code related to the routine
_nano_sys_clock_tick_announce() does not need the application of
typecasting.
Change-Id: I3d7374cd1a32aea7e4651726febde74ebe4ac8ac
Signed-off-by: Peter Mitsis <peter.mitsis@windriver.com>