Thanks, it worked and eveerything works smoothly now! 
I added an ifdef just in case:
#ifdef ui
#undef ui
#endif
FYI: not a critical error, but Make now fails with the following error at the end: make[2]: Nothing to be done for 'build/release-mingw32-x86.zip'. I currently don’t care, but perhaps something the devs should look into if they want an error free make procedure.