Can we completely remove WASM_BIGINT=0

[sbc100]

As of #27542 emscripten no longer supports targeting engines without Wasm BigInt integration.

However the WASM_BIGINT=0 is being kept around to enable -sWASM=0 (i.e. wasm2js).

If we were to add bigint support for wasm2js output then we could completely drop support for WASM_BIGINT=0 from emscripten.

The question is, are users of wasm2js deploying to engines without Bigint support?

This issue will act as the deprecation plan for WASM_BIGINT=0.

The process for deprecating and removing features from emscripten is laid out
in https://github.com/emscripten-core/emscripten/blob/main/CONTRIBUTING.md#deprecating-settings-and-features.

At any point in the process we may decide to delay or abort the deprecation and close this issue.

Deprecation checklist:

• Open an issue (this)
• Perform global search for usage in public repos
• Send message to emscripten-discuss
• Add "deprecation" warning to emcc
• Wait at least 4 releases or 2 months
• Remove feature from codebase

[juj]

Unity does use non-BigInt mode. It is marked deprecated, but still available.

In the next major release, we are planning of removing it, but it is a bit of time until that happens.

We don't use Wasm2JS anymore in production. I've tried to use it a couple of times to debug some nasty bugs, but unfortunately there are missing interactions with it (e.g. multithreading atomics), that prevented its use. If it did work with the more exotic features of Wasm, it could still be a productive lifesaver for deep debugging scenarios.