Along with this, will improve dt_t by replacing the TREE_LIST chain iteration with building up a constructor_elts vector (for efficiency when generating large data types).
Regards Iain
Next development goals are so weed out the rest of the functions
in IRState as of around the commit (link:
https://github.com/D-Programming-GDC/GDC/commit/ca497a421e8c37c240a6794e68c17225af75d9d6),
then rename IRBase over to IRState. During this course, some
general refactoring will be done, such as moving functions called
once into their callers, etc. The idea being that code
generation routines should not be dependent on IRState.
