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-2.12.1.orig/elf/dl-lookup.c glibc-2.12.1/elf/dl-lookup.c

 --- glibc-2.12.1.orig/elf/dl-lookup.c	2009-03-30 23:14:32.000000000 +0200

 +++ glibc-2.12.1/elf/dl-lookup.c	2009-11-13 00:51:36.000000000 +0100

 @@ -301,6 +301,12 @@

  	      /* FALLTHROUGH */

  	    case STB_GLOBAL:

 	    success:

 +#ifdef __mips__

 +	      /* HACK: MIPS marks its lazy evaluation stubs with SHN_UNDEF

 +		 symbols, we skip them. */

 +	      if (sym->st_shndx == SHN_UNDEF)

 +		break;

 +#endif

  	      /* Global definition.  Just what we need.  */

  	      result->s = sym;

  	      result->m = (struct link_map *) map;