arch/x86: prescott is an i686

let CT_ARCH_ARCH=prescott result in a i686 tuple prefix

Signed-off-by: Titus von Boxberg <titus@v9g.de>

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool"

reporter_comment=""