Fix up namespace usage to allow compiling in environments which globally define names also used in std.
Fix up namespace usage to allow compiling in environments which
globally define names also used in std.


Former-commit-id: 5fc602631ee731cfe67c5addc06a2154daadf8cd
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide