configure: add Core Text and DirectWrite to Libs.private
configure: add Core Text and DirectWrite to Libs.private

Fixes https://github.com/libass/libass/issues/211.

ShiftMediaProject/libass,astiob/libass,MrSmile/libass,astiob/libass,MrSmile/libass,ShiftMediaProject/libass,libass/libass,libass/libass