arch: add option to let gccdecide what floating point to use

Add an ARCH_FLOAT_AUTO option to avoid passing float options
to gcc and allow it to choose

Signed-off-by: Cody P Schafer <dev@codyps.com>
[yann.morin.1998@free.fr: slightly reword the commit log]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <088489641f4790262685.1399687813@localhost>
Patchwork-Id: 347584

 #!/bin/sh

 set -e

 printf "Running autoconf...\n"

 autoconf -Wall --force

 printf "Done. You may now run:\n    ./configure\n"