Update comments to indicate the ExternalCode API is not fully supported by the implementation.
Update comments to indicate the ExternalCode API is not fully
supported by the implementation.

kgnk/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide