Support platform=js/wasm

[t-hofmann]

Description

yet new to using "goxx" (started yesterday), I am not yet familiar with the internals. So I am not aware how much effort it would take to implement "js/wasm" as an additional target platform.

However it would be great if "webassembly" (js/wasm) would also be supported.

An implementation or hints to relevant places in the code would be appreciated.