bash: backport upstream security fix

BUG=chromium:417329
TEST=`VAR="() { ignored; }; /usr/bin/id" bash` no longer runs `id`

Change-Id: Ia51e1adf14ef8d64fa3a96a24f29a0ea6b5d7443
Previous-Reviewed-on: https://chromium-review.googlesource.com/219750
(cherry picked from commit dbd5f4fbce5327d79eb873cf931a2ff5e815bcf8)
Reviewed-on: https://chromium-review.googlesource.com/219754
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
3 files changed