wasm2js: Don't assume the existence of js assert function (#4357)

Its seems that with this emscripten change DCE is able to remove
the `assert` JS runtime function making this call to assert fail
with `ReferenceError: assert is not defined`.

Author: sbc100

src/wasm2js.h

@@ -2868,7 +2868,7 @@ void Wasm2JSGlue::emitSpecialSupport() {
     } else if (import->base == ABI::wasm2js::ATOMIC_RMW_I64) {
       out << R"(
   function wasm2js_atomic_rmw_i64(op, bytes, offset, ptr, valueLow, valueHigh) {
-    assert(bytes == 8); // TODO: support 1, 2, 4 as well
+    // TODO: support bytes=1, 2, 4 as well as 8.
     var view = new BigInt64Array(bufferView.buffer); // TODO cache
     ptr = (ptr + offset) >> 3;
     var value = BigInt(valueLow >>> 0) | (BigInt(valueHigh >>> 0) << BigInt(32));

test/wasm2js/atomics_32.2asm.js

@@ -40,7 +40,7 @@ memorySegments[1] = base64DecodeToExistingUint8Array(new Uint8Array(6), 0, "d29y
   }
 
   function wasm2js_atomic_rmw_i64(op, bytes, offset, ptr, valueLow, valueHigh) {
-    assert(bytes == 8); // TODO: support 1, 2, 4 as well
+    // TODO: support bytes=1, 2, 4 as well as 8.
     var view = new BigInt64Array(bufferView.buffer); // TODO cache
     ptr = (ptr + offset) >> 3;
     var value = BigInt(valueLow >>> 0) | (BigInt(valueHigh >>> 0) << BigInt(32));

test/wasm2js/atomics_32.2asm.js.opt

@@ -40,7 +40,7 @@ memorySegments[1] = base64DecodeToExistingUint8Array(new Uint8Array(6), 0, "d29y
   }
 
   function wasm2js_atomic_rmw_i64(op, bytes, offset, ptr, valueLow, valueHigh) {
-    assert(bytes == 8); // TODO: support 1, 2, 4 as well
+    // TODO: support bytes=1, 2, 4 as well as 8.
     var view = new BigInt64Array(bufferView.buffer); // TODO cache
     ptr = (ptr + offset) >> 3;
     var value = BigInt(valueLow >>> 0) | (BigInt(valueHigh >>> 0) << BigInt(32));