Fix build with CMake >= 3.28.0. FREETYPE_LIBRARY has not officially been
part of the user-facing interface of the FindFreetype module since CMake
2.6.0 [1] and has only been coincidentally defined up until this point.

[1] https://gitlab.kitware.com/cmake/cmake/-/commit/d18fb61c76c720ec5b1ac2cc4f30a5beaf071c33

--- src/cguittfont/CMakeLists.txt.orig	2023-12-26 21:52:39 UTC
+++ src/cguittfont/CMakeLists.txt
@@ -24,6 +24,6 @@ target_link_libraries(
 target_link_libraries(
 	cguittfont
 	${IRRLICHT_LIBRARY}
-	${FREETYPE_LIBRARY}
+	${FREETYPE_LIBRARIES}
 	${ZLIB_LIBRARIES}  # needed by freetype, repeated here for safety
 	)