glibc: Fix assertion failure when using incompatible locale data

Borrowed from

  http://git.savannah.gnu.org/cgit/guix.git/plain/gnu/packages/patches/glibc-locale-incompatibility.patch

https://github.com/NixOS/nix/issues/599

We may also want to apply

  http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/patches/glibc-versioned-locpath.patch

but we'll need to ditch locale-archive first. (Apparently
locale-archive is not very useful anymore anyway.)