Print warnings to stderr instead of stdout
Print warnings to stderr instead of stdout


Former-commit-id: 759727e8c8a80b115e93d217390564277df7d17d
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide