python: Fix compareVersions for python 3.

python: Fix compareVersions for python 3.

When the internal utility function make_version_list sees a string, it
tries to convert it into a list using the map() function. In python 3,
that returns an iterator. The following call to zip() will consume those
iterators, and then the following calls to len() will die because they
don't work on map iterators.

This is only a problem if all the common components of the version lists
are equal, and the comparison needs to then check if one of the lists
was equal to the other but with more components. When versions are
equal, for instance when compiling with the oldest supported version of
gcc (4.8.0) this error surfaces and breaks our scons build.

A simple fix is to just wrap the call to map() with list() to convert
the iterator to a flat list, making the other logic work as before.

Change-Id: If9dc5cd7fff70c21229ac3dd9a017edeccd26148
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28309
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>