Need .expr for builtin::memset
Updated TODO with builtin
Updated test - set other parts of the array
s/int .*_size/unsigned&/
s/type_ref_new.../type_ref_cached/
Better __builtin_memset - see commit message

Use the largest type we can for zeroing the memory,
then pad leftovers.
Moved working tests to test2/
General object creation test
Global inits are folded and casted in one
Global array-range initialisers
Working local/stack range evaluate-once initialisers (scalars only)