fix cmake rules for lesson 10
fix cmake rules for lesson 10

It used the Generator ruleset, which happened to mostly work, but
basically by sheer luck, since the arguments passed to the “generator”
were ignored; since this lesson is (explicitly) *not* a Generator, it
should show the real steps necessary, and not attempt to leverage the
Generator machinery.


Former-commit-id: 5ec44551f19a873f6a2445d679fdbbbc6a0a54f7
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide