[gccgo] Add complex numbers

[Richard Henderson]

> +    case OPERATOR_MULT:
> +      {
> +	// You might think that multiplying two complex numbers would
> +	// be simple, and you would be right, until you start to think
> +	// about getting the right answer for infinity.  If one
> +	// operand here is infinity and the other is anything other
> +	// than zero or NaN, then we are going to wind up subtracting
> +	// two infinity values.  That will give us a NaN, but the
> +	// correct answer is infinity.
...

We already require the mpc library.  Surely some of this 
can be simplified...


r~