Emscripten with pthreads generates empty arrow functions `{}` for callback
paths it assumes won't be used. However, when registering HTML5 events from
the main browser thread, targetThread is 0 and the direct call path IS taken.
This fix post-processes the generated JS to replace empty callbacks with
actual dynCall invocations for:
- HTML5 event callbacks (dynCall_iiii) - 7 instances
- pthread entry points (dynCall_ii) - 1 instance
- Signal handlers (dynCall_vi) - 1 instance
- Async timers (dynCall_vi) - 1 instance
Also improves build logging to show completion status and exit code.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
014816b7a5