config: fix generated config files when GREP_OPTIONS set --color=always

grep is used when generating some .in files (in config.gen). If GREP_OPTIONS
contains --color=always, then the generated files will contains some escape
sequences setting the color, and mconf would choke on those escape sequences.

Always set and export an empty GREP_OPTIONS to avoid that.

Issue reported by Kevin Kirkup <kevin dot kirkup at gmail dot com> :
http://sourceware.org/ml/crossgcc/2009-12/msg00026.html

 --- binutils/ld/emulparams/elf_i386.sh

 +++ binutils/ld/emulparams/elf_i386.sh

 @@ -13,3 +13,13 @@

  NO_SMALL_DATA=yes

  SEPARATE_GOTPLT=12

  IREL_IN_PLT=

 +

 +# In Gentoo, we install 32bit libs into /lib32 in an

 +# ABI setup with amd64/x86

 +case "$target" in

 +  x86_64*-linux*)

 +    case "$EMULATION_NAME" in

 +      *i386*) LIBPATH_SUFFIX=32  ;;

 +    esac

 +  ;;

 +esac