CMake: define HALIDE_NO_JPEG / HALIDE_NO_PNG automatically
CMake: define HALIDE_NO_JPEG / HALIDE_NO_PNG automatically

Former-commit-id: b9f9255eae9391b5ba9852cdc59558b8c72975b6
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide