Comment 1 for bug 72635

The API changed with freetype-2.2 and later versions and "include/freetype/internal/" is NOT
copied to the headers installed. From the file freetype-2.3.1/docs/CHANGES:

    - Version 2.2 no longer exposes its internals, this is, the header
      files located in the `include/freetype/internal' directory of
      the source package are not copied anymore by the `make install'
      command. Consequently, a number of rogue clients which directly
      access FreeType's internal functions and structures won't
      compile without modification.

      We provide patches for most of those rogue clients. See the
      following page for more information:

        http://www.freetype.org/freetype2/patches/rogue-patches.html

So Inkscape, other apps that bomb out should be using patches or get updated.