prerm is in libnewlib-arm-none-eabi 2.2.0+git20150830.5a3d536-1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23  | #!/bin/sh
set -e
case "$1" in
  # only remove in remove/deconfigure so we don't disrupt users' preferences
  remove|deconfigure)
    update-alternatives --quiet --remove \
        gcc-arm-none-eabi-lib \
        /usr/lib/arm-none-eabi/newlib
    ;;
  upgrade|failed-upgrade)
    ;;
  *)
    echo "prerm called with unknown argument \`$1'" >&2
    exit 0
    ;;
esac
exit 0
 |