i386.md fix

[Joern Rennecke]

> This is patch to remove addqi_low_1 pattern from i386.md.  I am not quite
> sure, why it has been added (no splitters seems to result to it), but it
> causes problems with reload, since in/out operand is matched with input
> one making them impossible to reload properly. In case we want gcc to be able
> to generate such an "partial" arithmetic, this would require more work in
> combine, different representation and to add rest of arithmetic patterns of
> that form.

Have you tried to change the '+' into an '=' ?