altos: Check pdata+xdata memory usage during build

altos: Check pdata+xdata memory usage during build

The sdcc linker doesn't check the sum of pdata+xdata memory usage, it
only ensures that xdata itself is small enough. This doesn't keep
xdata below the end of usable ram on the cc1111 though (0xfe000).

Fix up the check-stack program to also make sure all of xdata fits in
available memory.

Signed-off-by: Keith Packard <keithp@keithp.com>