[3.x] [HTML5] Add GDNative+Threads build.

[Faless]

Requires an unreleased version of emscripten (or more correctly, a recent LLVM patch, see: emscripten-core/emscripten#17150 and https://reviews.llvm.org/D127333).

You can try it out by building LLVM from source, and overriding the LLVM version used by emscripten via the EM_LLVM_ROOT env variable (see here).

Only template versions work, the editor fails to start (possibly related to emscripten-core/emscripten#15487):

WebAssembly.instantiate(): imports count of 132022 exceeds internal limit of 100000

Will open on a dedicated PR for master soon.

[akien-mga]

Changes look good. Given that it requires bleeding edge Emscripten and LLVM I guess it's a bit late for 3.5, we can likely merge this for 3.6?

[Faless]

Changes look good. Given that it requires bleeding edge Emscripten and LLVM I guess it's a bit late for 3.5, we can likely merge this for 3.6?

I know it's very late, I was thinking maybe we could provide official builds in a point release (e.g. 3.5.1), but we can re-target for 3.x and backport it later on in case.

[akien-mga]

Changes look good. Given that it requires bleeding edge Emscripten and LLVM I guess it's a bit late for 3.5, we can likely merge this for 3.6?

I know it's very late, I was thinking maybe we could provide official builds in a point release (e.g. 3.5.1), but we can re-target for 3.x and backport it later on in case.

Yeah I mean the changes seem harmless enough so I don't mind merging it for 3.5 to enable in a point release later. But then we should maybe unexpose the "Threads and GDNative" export option to avoid confusion, as we won't be providing templates for it in 3.5.stable.

You could keep it implemented but just not part of the property enum hint (and people who want to test with custom builds could set the value manually in their export_presets.cfg).

[akien-mga]

Thanks!