* msp430/msp430-sim.ld (.stack): Add an assertion to make sure
that the data area does not overrun the stack. PROVIDE a new
symbol __stack_size to allow the user to set the limit.
* msp430/msp430xl-sim.ld (.stack): Likewise.
* rl78/rl78-sim.ld (.stack): Likewise.
* rl78/rl78.ld (.stack): Likewise.
* rx/rx-sim.ld (.stack): Likewise.
* rx/rx.ld (.stack): Likewise.