Add cases with long long a, b in hexadecimal, where it is more obvious
whether or not a + b or a - b carries to or borrows from bit 32. Add
failure codes to identify each case.
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.