Excepted the cpp directory from hygiene tests.
Excepted the cpp directory from hygiene tests.

Former-commit-id: 4a38c695eaa3654d63057a56f8f7072f8c612fcf
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide