You can't terminate char * varargs with 0, since it will
be the wrong width on 64-bit platforms. You need to use
(char *)0 or NULL. (I'm not sure NULL, strictly speaking,
is guaranteed to work by the C standard, but practically
speaking it works universally and will continue to work
universally because much software depends on it.)
os = FcObjectSetBuild (FC_FAMILY, FC_STYLE, 0);
Seems to be the only instance in fontconfig or Xft.
Thanks for finding this one.