Minor cleanup in CMakeLists.txt of src.
Minor cleanup in CMakeLists.txt of src.

retuxx/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,retuxx/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,retuxx/tinyspline