CMake doesn't recognize it properly on windows.
1) the header detection on a directory "freetype" fails, it seems to
need a filename: "ft2build.h" actually works.
2) the 3rdparty I am supplying for FlightGear contains freetype-2.3.4. I
added the correct library naming for this particular release.
I double-checked my directory layout with the 3rdparty supplied by other
OSG contributors."
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