RFR: 8224851: AArch64: fix warnings and errors with Clang and GCC 8.3

[Nick Gasson]

Hi Kim,

Kim Barrett writes:
>
> I think the solution here is to use placement new, but explicitly qualified to actually get there, e.g.
>
> ::new (reg_map) RegisterMap(map);
>
> Using unqualified new will do the lookup in RegisterMap, find some declarations in StackObj (but not the one we want) and fail.
> This is a pretty common pattern.
>

This works, thanks.


Nick