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)

diff -durN glibc-2.7.orig/Makerules glibc-2.7/Makerules

--- glibc-2.7.orig/Makerules	2007-08-26 04:18:03.000000000 +0200

+++ glibc-2.7/Makerules	2008-07-28 15:17:27.000000000 +0200

@@ -1203,6 +1203,9 @@

 # The include magic above causes those files to use this variable for flags.

 CPPFLAGS-nonlib = -DNOT_IN_libc=1

+ifneq ($(OBJDUMP_FOR_HOST),)

+OBJDUMP = $(OBJDUMP_FOR_HOST)

+endif

 ifeq ($(versioning),yes)

 # Generate normalized lists of symbols, versions, and data sizes.