GMAT can be configured and compiled using CMake. However, these build scripts are still under construction. Here is documentation on the CMake system.
Using the GSFC-Internal CMake Build System
Here are instructions about using the updated CMake-based build system (currently GSFC-internal)
How to Build Scripts on Windows 7/8, Linux Ubuntu 12.04 and Macintosh OSX Lion systems
Here are instructions about Building GMAT on Windows, Linux and Macintosh systems.