I integrated this build into my project and ran into a minor problem in trying to use an arial truetype font. Lines 171 - 173 of \src\sfnt\ttmtx.c, in the tt_face_load_hmtx method look like this:
The problem is that my font has all 1673 long format metrics and 0 short format so the second call to FT_QNEW_ARRAY gets 0 as its second argument. This causes it throw an invalid parameter error. I'm not exactly sure what the intention was but I think all long or all short formats should be valid.