Added test running GPU tiles nested within parallel loop
Added test running GPU tiles nested within parallel loop


Former-commit-id: 51451f0f2147ac4b06844021a4b7af7a8882aac6
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide