We can't cleanup the environment like e.g. sudo would do as you usually
want the environment to "leak" into these helpers, but some variables
like HOME should really not have still the value of the root user – it
could confuse the helpers (USER) and HOME isn't accessible anyhow.
We need to ignore messages from gcov. All those messages
start with profiling: and are printed using vfprintf(), so
the only thing we can do is add a library overriding those
functions and linking apt-pkg to it.