PR11867, bignum operations

[DJ Delorie]

> So it is.  I checked the chip docs this time..
> gas/configure.tgt had it as big, CGEN_ENDIAN_BIG is passed to
> m32c_cgen_cpu_open and tc-m32c.h has #define TARGET_BYTES_BIG_ENDIAN 1.

The CGEN stuff is fragile, as it's using the endianness to represent
the *opcode* not the *data*.  I wouldn't change anything without a
really good reason :-)

What was actually broken that triggered all this?