loader: Move back __libc_stack_end to the loader.

The exact location of the stack end is not needed by java so move back this
variable to restore the state to what was done before the mkfs.so/cpiod.so split.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>