WIP Added libtess library extracted from

https://cgit.freedesktop.org/mesa/glu/
The library is stable (it should be, since it is in use since 1994),
but it is not thread safe: Its callbacks do not receive any pointer
to a context.

src/glu-libtess/CMakeLists.txt

@@ -0,0 +1,36 @@
+project(glu-libtess)
+cmake_minimum_required(VERSION 2.6)
+
+add_library(glu-libtess STATIC 
+	src/dict-list.h
+	src/dict.c
+	src/dict.h
+	src/geom.c
+	src/geom.h
+	src/gluos.h
+	src/memalloc.c
+	src/memalloc.h
+	src/mesh.c
+	src/mesh.h
+	src/normal.c
+	src/normal.h
+	src/priorityq.c
+	src/priorityq.h
+	src/priorityq-heap.h
+	src/priorityq-sort.h
+	src/render.c
+	src/render.h
+	src/sweep.c
+	src/sweep.h
+	src/tess.c
+	src/tess.h
+	src/tessmono.c
+	src/tessmono.h
+	include/glu-libtess.h
+	)
+
+if(UNIX)
+    target_link_libraries(glu-libtess m)
+endif(UNIX)
+
+target_include_directories(glu-libtess PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)