Add an explanatory comment on Block::make multi-statement variant.
Add an explanatory comment on Block::make multi-statement variant.

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