PATCH: enable dfp constant folding

[Roger Sayle]

On Sat, 4 Feb 2006, Ben Elliston wrote:
> 2006-02-04  Ben Elliston  <bje@au.ibm.com>
>
>         * dfp.c (decimal_real_arithmetic): Change second argument type
>         from int to enum tree_code. Do not always return true, but now
>         return result of any call to decimal_do helper functions.
>         * dfp.h (decimal_real_arithmetic): Update prototype.

This is OK for mainline.

Roger
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