Changes to the makefile to get the nightly tests to pass
Changes to the makefile to get the nightly tests to pass

1) Add -lcuda and similar for the gpu tests

2) Don't build the generators with build_tests. build_tests
doesn't currently run any Halide code. I.e. it's supposed to
build the generators, but not run them yet. With this change
it does neither, which isn't ideal.


Former-commit-id: ce64f44b13df406fc9c6501da3654a58b2dc7291
Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide