We are not using any alloc function that respects that variable, so
lets drop it. Backport of this commit:

  commit 0ce61e21d6d7dcca0090e319bbcdb678570f2c3f
  Author: Adam Jackson <ajax@redhat.com>
  Date:   Fri Oct 3 16:05:19 2008 -0400

    Remove the Must_have_memory hack.

    Also remove an astonishing amount of misunderstanding of how casts work.