Skip the long-long test set on other platforms, because they don't
have long long. Each platform would need to implement 8-byte
operations like `adi 8` in its code generator, and set long long to
8 bytes in its descr file.
The first test is for negation, addition, and subtraction. It also
requires comparison for equality.
was nearly useless; lots of fixes to qemuppc and pc86 sbrk(), which was broken;
change the pc86 console to echo output to the serial port (needed for running
tests on qemu).