Added the beginnings of a unit tester.
Added the beginnings of a unit tester.

Currently just calls IRPrinter's test


Former-commit-id: 9cfac9ebc9dc448db11f70b9715c8f6eb85ebff7
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide