Somtimes, building the freetype library failes due to circular dependencies between the
harfbuzz and the
freetype libraries depending on the set USE flags. This can be solved by the following order of installation:
USE="-harfbuzz" emerge -1 media-libs/freetype emerge -1 media-libs/harfbuzz emerge -1 media-libs/freetype
Future updates should work without any further issues though.