Don't copy etc/config.guess for binutils{,_*}.
    
    etc/README.md: updated.
    midipix.env:${DEFAULT_BUILD_VARS}: adds AUTOCONF_CONFIG_GUESS.
    groups/010.host_deps.group:binutils_build:${PKG_PATCHES_EXTRA}: from chainport (via midipix.)
    patches/binutils_build-2.24.51.local.patch: from patches/binutils-2.24.51.local.patch (via midipix.)
    subr/pkg_configure_autotools.subr: copy etc/config.guess according to ${PKG_AUTOCONF_CONFIG_GUESS}.