Multiple ORed values in CONSTANT_CLASSES.to_string

This is mostly implemented for clGetKernelArgInfo called with CL_KERNEL_ARG_TYPE_QUALIFIER. In this case, the value can be a bitwise or of different type qualifiers (e.g. const and volatile), so we need to go through all of them.

Not sure this is the right fix, since it could be a change in behavior for anyone checking the output. I ran it with the concurrency checker through pytential and it didn't crash anything.