Strange...
The ImageMagick source package for Windows comes with FreeType version 2.1.5 (2003-09-02) but the latest version of FreeType is 2.3.5 (2007-07-02). I was trying to update it, but the "original" version comes with a folder named "autohint" and the downloaded library doesn't.
Anyway, to save hours of work and headaches, I decided to keep using the older version for the Windows build. Everything is now compiling correctly.
Now I will try to make the debug version. Wish me luck...