Move WasmFS threading heartbeat to library JS code [NFC] (#19697)

This is consistent with other calls into JS code from WasmFS, and it
removes the single EM_ASM from the codebase.

Noticed because the EM_ASM caused a test not to pass (see added comment
in test code).

Author: kripken

src/library_sigs.js

@@ -414,6 +414,7 @@ sigs = {
   _wasmfs_opfs_set_size_access__sig: 'vpijp',
   _wasmfs_opfs_set_size_file__sig: 'vpijp',
   _wasmfs_opfs_write_access__sig: 'iipii',
+  _wasmfs_thread_utils_heartbeat__sig: 'vp',
   abort__sig: 'v',
   alBuffer3f__sig: 'viifff',
   alBuffer3i__sig: 'viiiii',

src/library_wasmfs.js

@@ -416,4 +416,15 @@ FS.createPreloadedFile = FS_createPreloadedFile;
   _wasmfs_copy_preloaded_file_data: function(index, buffer) {
     HEAPU8.set(wasmFSPreloadedFiles[index].fileData, buffer);
   },
+
+  _wasmfs_thread_utils_heartbeat: (queue) => {
+    var intervalID =
+      setInterval(() => {
+        if (ABORT) {
+          clearInterval(intervalID);
+        } else {
+          _emscripten_proxy_execute_queue(queue);
+        }
+      }, 50);
+  },
 });

system/lib/wasmfs/thread_utils.h

@@ -13,6 +13,10 @@
 #include <emscripten/proxying.h>
 #include <emscripten/threading.h>
 
+extern "C" {
+void _wasmfs_thread_utils_heartbeat(em_proxying_queue* ctx);
+}
+
 namespace emscripten {
 
 // Helper class for synchronously proxying work to a dedicated worker thread,
@@ -51,16 +55,7 @@ class ProxyWorker {
         //
         // Note that this requires adding _emscripten_proxy_execute_queue to
         // EXPORTED_FUNCTIONS.
-        EM_ASM({
-          var intervalID =
-            setInterval(() => {
-              if (ABORT) {
-                clearInterval(intervalID);
-              } else {
-                _emscripten_proxy_execute_queue($0);
-              }
-            }, 50);
-          }, queue.queue);
+        _wasmfs_thread_utils_heartbeat(queue.queue);
 
         // Sit in the event loop performing work as it comes in.
         emscripten_exit_with_live_runtime();

test/test_other.py

@@ -9079,8 +9079,11 @@ def test_js_optimizer_parse_error(self):
   });
 }
 ''')
-    stderr = self.expect_fail([EMCC, 'src.c', '-O2'])
-    # wasm backend output doesn't have spaces in the EM_ASM function bodies
+    stderr = self.expect_fail([EMCC, 'src.c', '-O2'] + self.get_emcc_args())
+    # TODO: To make this test work in WasmFS, the constant below must be
+    #       modified. It is the address in memory of the string constant of the
+    #       EM_ASM, and WasmFS has its own string constants that cause a
+    #       difference.
     self.assertContained(('''
   1024: () => { var x = !<->5.; }
                          ^