PATCH: Update default arch for x86

[Jason Merrill]

On 02/27/2010 07:00 AM, Joseph S. Myers wrote:
> If 64-bit support is required, whether for a target with 64-bit multilibs
> by default or where enabled by --enable-targets=all, using an i686-*
> target should mean --with-arch-32=i686 without implying any particular
> --with-arch-64 option.

That makes sense, but x86-64 is the same default supplied by i386.c, so 
I believe the effect is the same.

Jason