Global const data
=================

SLUL will not have global mutable data.
But it will have global constant data (e.g. a constant array of bytes).

Requirements for globals:
1. Must be constant/immutable.
2. Must be compile-time constants / Cannot have initializers.
3. Must not be (or contain) references
   (that would require initializers / would not be compile-time constant)
4. Must be architecture-independent
   (otherwise it can overflow or create an invalid array index on
    some platforms, but not on other).

Problems:

"wuint i = large_number + 1"
"int i = large_number + 1"
    - this gives different behavior depending on the size of int.
    - requiring int = 32 bits is probably a very good idea anyway,
      except for embedded platforms.
    => forbid wuint in const-exprs if "\option allow16" is in enabled?