Error on wasm worker creation when SAB is not available

This should have been part of emscripten-core#22710

Author: sbc100

src/library_wasm_worker.js

@@ -137,7 +137,6 @@ addToLibrary({
   // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src#unsafe_eval_expressions
   $_wasmWorkerBlobUrl: "URL.createObjectURL(new Blob(['onmessage=function(d){onmessage=null;d=d.data;{{{ captureModuleArg() }}}{{{ instantiateWasm() }}}importScripts(d.js);{{{ instantiateModule() }}}d.wasm=d.mem=d.js=0;}'],{type:'application/javascript'}))",
 #endif
-
   _emscripten_create_wasm_worker__deps: [
     '$_wasmWorkers', '$_wasmWorkersID',
     '$_wasmWorkerAppendToQueue', '$_wasmWorkerRunPostMessage',
@@ -156,6 +155,12 @@ if (ENVIRONMENT_IS_WASM_WORKER
   addEventListener("message", _wasmWorkerAppendToQueue);
 }`,
   _emscripten_create_wasm_worker: (stackLowestAddress, stackSize) => {
+    if (typeof SharedArrayBuffer == 'undefined') {
+#if ASSERTIONS
+      dbg('create_wasm_worker: environment does not support SharedArrayBuffer, wasm workers are not available');
+#endif
+      return 0;
+    }
     let worker = _wasmWorkers[_wasmWorkersID] = new Worker(
 #if WASM_WORKERS == 2
       // WASM_WORKERS=2 mode embeds .ww.js file contents into the main .js file

test/code_size/hello_wasm_worker_wasm.js

@@ -15,6 +15,7 @@ c && (m[0] = this, addEventListener("message", l));
 WebAssembly.instantiate(b.wasm, {
     a: {
         b: (a, d) => {
+            if ("undefined" == typeof SharedArrayBuffer) return 0;
             let r = m[n] = new Worker(b.$wb);
             r.postMessage({
                 $ww: n,

test/code_size/hello_wasm_worker_wasm.json

@@ -1,12 +1,12 @@
 {
   "a.html": 618,
   "a.html.gz": 384,
-  "a.js": 665,
-  "a.js.gz": 455,
+  "a.js": 715,
+  "a.js.gz": 484,
   "a.ww.js": 115,
   "a.ww.js.gz": 127,
   "a.wasm": 1850,
   "a.wasm.gz": 1050,
-  "total": 3248,
-  "total_gz": 2016
+  "total": 3298,
+  "total_gz": 2045
 }