Adds the attributes nounwind and willreturn to all function
declarations. Adds `memory(none)` equivalent to the id/dimension
function declarations. The function declaration attributes are copied to
the function calls.
`nounwind` is legal because there are no exception in SPIR-V. I also do
not see any reason why any of these functions would not return when used
correctly.
I'm confident that the get id/dim functions will have no externally
observable memory effects, but think the convergent functions will have
effects.
5a53add85a