Revisit `volatile` qualifiers on checked types

[lenary]

C11 allows volatile-qualified types, we should make sure their constraints are reasonable, and if not add some for volatile-qualified checked types.

One proposal of mine is to ban any volatile checked types, with the understanding that volatile types are for interacting with specific hardware protocols, or somewhere where the programmer doesn't want to compiler to interfere, and therefore the programmer should use unchecked volatile types, but then assign the resulting values of operations with them into variables with checked types, before they go further into the program.