gnu: bash: Update to 4.3.27 and fix out-of-bounds memory accesses.

Based on a patch by Ludovic Courtès <ludo@gnu.org>.

* gnu/packages/bash.scm (%patch-series-4.3): Add two patches.
  (bash)[source]: Add parser-oob patch.  Add 'snippet'.
  [native-inputs]: New field.
* gnu/packages/commencement.scm (bison-boot1): New variable.
  (static-bash-for-glibc): Add 'native-inputs'.

Co-Authored-By: Ludovic Courtès <ludo@gnu.org>