scripts: unset CONFIG_SITE

Some distributions (eg. openSUSE 12.1) systematically export
the CONFIG_SITE environment variable to point to a custom
script setting misc paths for ./configure.

This can, and does, break when cross-compiling for architectures
that are not supported by this script.

The simple workaround is to unset this variable.
NB: buildroot has a similar fix:
http://git.buildroot.org/buildroot/commit/?id=12c9f7dd6dee9c6029b4f9a12d6aac1516911ab4

Reported-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 21f4f28e60ec0342133086c9a51e7f0e5b181fb8)

http://sourceware.org/ml/binutils/2007-07/msg00401.html

http://sourceware.org/bugzilla/show_bug.cgi?id=4970

diff -durN binutils-2.20.1.orig/configure binutils-2.20.1/configure

--- binutils-2.20.1.orig/configure	2010-03-03 14:59:02.000000000 +0100

+++ binutils-2.20.1/configure	2010-08-17 19:32:05.000000000 +0200

@@ -6466,6 +6466,7 @@

   *-*-mingw* | *-*-cygwin ) RPATH_ENVVAR=PATH ;;

   *) RPATH_ENVVAR=LD_LIBRARY_PATH ;;

 esac

+RPATH_ENVVAR="cant_touch_this_nah_nah_nah"

 # On systems where the dynamic library environment variable is PATH,

 # gcc/ will put dynamic libraries into a subdirectory to avoid adding