OpenCL targets aren't aware of some math built-ins

[zachjweiner]

I see the new function interface is much more careful about what's in the namespace (which is great!), but I think a number of the built-in math functions aren't currently registered. I tried to hack in, e.g., round to the lists of functions in target/opencl.py and target/pyopencl.py (e.g., here and here) but it still appeared to be unrecognized. If someone can point me in the right direction, I'd be happy to add the missing built ins.

[zachjweiner]

Apparently the nonresolvedness was being cached, so the above actually should work. Will open a PR, then!