(b) don't override the delete operator (on top of the regular conditions for
stack allocation that also apply to arrays, structs, etc.).
The "no destructor" clause is not strictly necessary, but calling them at the
right time would be tricky to say the least; it would involve, among other
things, "manually" inserting a try-finally block around anything that might
throw exceptions not caught in the current function.
Note: objects with custom new operators are automatically ignored because they
don't use the regular allocation runtime call, so there's no need to pay special
attention to them.
This one promotes GC allocations to stack memory when it can determine it's safe
to do so.
Not all GC calls are recognized yet (in fact only one *is* recognized for now).
Needs metadata, so disabled for LLVM versions that don't support it.
