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

 call_to=@@DEFAULT_LD@@

 case "${CTNG_LD_IS}" in

     bfd)    call_to=bfd;;

     gold)   call_to=gold;;

 esac

 exec "${0}.${call_to}" "$@"

 exit $?