[Web] Add workaround for missing export in threaded builds

The offending symbol gets stripped away by wasm-dce but it's used on the
JavaScript side and causes and undefined symbol which also causes the
closure compiler to throw an error.

platform/web/detect.py

@@ -227,6 +227,11 @@ def configure(env: "SConsEnvironment"):
         env.Append(LINKFLAGS=["-sDEFAULT_PTHREAD_STACK_SIZE=%sKB" % env["default_pthread_stack_size"]])
         env.Append(LINKFLAGS=["-sPTHREAD_POOL_SIZE=8"])
         env.Append(LINKFLAGS=["-sWASM_MEM_MAX=2048MB"])
+        if not env["dlink_enabled"]:
+            # Workaround https://github.com/emscripten-core/emscripten/issues/21844#issuecomment-2116936414.
+            # Not needed (and potentially dangerous) when dlink_enabled=yes, since we set EXPORT_ALL=1 in that case.
+            env.Append(LINKFLAGS=["-sEXPORTED_FUNCTIONS=['__emscripten_thread_crashed','_main']"])
+
     elif env["proxy_to_pthread"]:
         print_warning('"threads=no" support requires "proxy_to_pthread=no", disabling proxy to pthread.')
         env["proxy_to_pthread"] = False