distro: glibc: Build the statically-linked Bash embedded in glibc.

* distro/packages/base.scm (glibc): Expect "static-bash" to be a
  directory, not a single file.  Call `remove-store-references' on the
  "bash" binary that is copied.  Add an `sh' -> `bash' symlink.  Change
  the "static-bash" input to (static-package bash-light).
  (glibc-final): Rename to...
  (glibc-final-with-bootstrap-bash): ... this.  Change `name' to
  "glibc-intermediate".  Remove #:patch-shebangs? setting.
  (cross-gcc-wrapper): New procedure, with code formerly in
  GCC-BOOT0-WRAPPED.
  (gcc-boot0-wrapped): Use it.
  (static-bash-for-glibc): New variable.
  (glibc-final): Inherit from GLIBC-FINAL-WITH-BOOTSTRAP-BASH, and use
  STATIC-BASH-FOR-GLIBC as the "static-bash" input.