I'm pretty sure I am not editing Makefile.mingw correctly (I don't really speak make). You were right about not cleaning properly earlier though, because it turns out the edit to Text.cpp/h I mentioned was not necessary.
Anyway
this is the makefile I'm attempting to use (I only edited the paths to SDL, Boost and YAML). Again, fairly sure it's to do with YAML because the makefile points to sources that don't exist.