Remove a __wasm__ define guard around public APIs

[rdw-software]

Hi,

while writing LuaJIT bindings for this library I noticed something peculiar:

• In this merged PR certain wasm APIs were made public in the header file only
• The implementation itself is however still guarded by the WebAssembly define
• As a result, the define is still present in the latest release, which I've been using

Accordingly, I'm unable to bind these functions (without hacks). This PR should fix the problem, hopefully without side effects.

Since I'm not sure about the wasm stuff I simply moved the define upwards instead of completely deleting it.