gnu: glibc: Fix 'ldd' on x86_64.

Reported by Cyril Roelandt at
<https://lists.gnu.org/archive/html/guix-devel/2013-09/msg00136.html>.

* gnu/packages/patches/glibc-ldd-x86_64.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/base.scm (glibc): Use it.