Can you make configure look for development files of libexpat in PATH and use the shipped source files only if nothing was found? The main reason is that when you're creating packages for Debian systems, an embedded expat library is considered a bug.
Is there a reason why Aleph One is embedding libexpat?
I can think of three reasons why it would need to be statically linked:
1. The system doesn't have an expat library installed.
2. The system's expat library is out-of-date and won't work.
3. The source of expat used has binary-incompatible changes that won't work with a standard version.
The version in the source tree is 2.0.1 which is used in Debian Oldstable and Ubuntu 12.04 too. Ubuntu 14.04, Debian Stable and newer versions use 2.1.0. When I did link a build against the system's libexpat it actually worked and I could run Marathon on it.
FYI, I'm looking to remove expat entirely in favor of Boost.PropertyTree's XML parser, which would solve the issue in a different way.