WebAssembly + Custom Runtime + Associative Arrays

[kinke]

Ouch, it's compiler bug - the compiler's hardcoded prototype for 
_aaInX() uses a `void*` as first param, not a `AA` struct 
wrapping the impl pointer. So this assumes the ABI/calling 
convention treats both types identically, which isn't currently 
the case for LDC's wasm ABI.

So using `void* _aaInX(AAImpl* aaimpl, ...)` works around this.