The GTK buildbot is repeatedly failing. These are the errors: error: unicode/uchar.h: No such file or directory error: unicode/ustring.h: No such file or directory error: unicode/utf16.h: No such file or directory Someone told me this is a build slave configuration problem.
Alp has landed an attempted fix in r30991. I'll keep an eye on the buildbots and close this if it does fix the problem.
This is now working.