distro: Change the module name space to (gnu ...).

* distro: Rename to...
* gnu: ... this.  Update module names accordingly.
* Makefile.am: Adjust accordingly.
* po/POTFILES.in: Likewise.
* distro.scm: Search for files under /gnu/packages instead of
  /distro/packages.
* gnu/packages/base.scm (ld-wrapper-boot3): Likewise.

distro: Patch libc to avoid accessing /etc/ld.so.cache and friends.

* distro/packages/base.scm (glibc): Apply `glibc-no-ld-so-cache.patch'.
  (glibc-final): Inherit GLIBC's inputs.
* distro/packages/patches/glibc-no-ld-so-cache.patch: New file.
* Makefile.am (dist_patch_DATA): Add it.