SINGLE_FILE and pthread incompatibility

According to https://github.com/emscripten-core/emscripten/pull/12833#issue-746884561 which says the following:

> SINGLE_FILE=1 is not supported with Wasm Workers (like it is not supported with pthreads)

I'm unable to find other specific documentation for pthreads not supporting SINGLE_FILE, but locally I can confirm that removing SINGLE_FILE does indeed fix the threading issue I'm running into (where the thread does not get executed with `detach`).

What is the specific reason(s) that SINGLE_FILE does not work with pthreads? From what I understand about SINGLE_FILE, it adds the contents of the .js and .wasm files (as a Base64 string) into the HTML file as opposed to reading the wasm contents via locateFile - clearly there is something else that I'm missing.

まず、リンクされている Emscripten のプルリクエストを読み、SINGLE_FILE=1 の有無による報告済みの pthreads の動作を比較します。関連する Emscripten のエントリポイントで、SINGLE_FILE、locateFile、Wasm Workers がどのように連携するかを追跡します。SINGLE_FILE が pthreads と互換性を持たない具体的な理由を文書化し、サポートされる構成を明確にできれば完了です。

索引モデルが issue の本文から書いたものです。