Call __main_void if exported by a plugin.

[PiotrSikora]

This is how Rust exports main() function since Rust v1.67.

[leonm1]

Should we include a test for this?

[PiotrSikora]

Should we include a test for this?

Sure, I'll add it.

But we don't really have tests for any of the start functions here... and we have exactly zero integration tests with real SDKs in this repo, only plain Wasm modules... Maybe you have some cycles to add them?

[PiotrSikora]

Actually, this turns out to be tricky.

We need to use nightly channel (bazelisk --@rules_rust//rust/toolchain/channel=nightly) to build Wasm reactors, but this can be only done globally and not on a per-target basis, so adding this flag would also affect Wasmtime build... but since this would be limited only to builds within this repo and not affect embedders, perhaps that's fine?

But my vote would be to skip this test altogether, since we don't test the other entrypoints anyway.

[PiotrSikora]

Reverted the code back to originally approved testless version.