Split emit_file into 3.7 and legacy pre-3.7 versions
Split emit_file into 3.7 and legacy pre-3.7 versions


Former-commit-id: 7272576ca022fcc0650846b76408fd90b977c2aa
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide