[WebAssembly] Temporarily work around lack of __attribute__((constructor))

We don't have a great way to ensure that the current-global-actor hook
will get installed by the concurrency library with WebAssembly, so
temporarily work around the issue by relying on the fact that we also
aren't doing actual concurrency with WebAssembly.

Author: DougGregor

stdlib/public/runtime/ProtocolConformance.cpp

@@ -1392,8 +1392,17 @@ static bool swift_isInConformanceExecutionContextImpl(
     return true;
 
   if (context->globalActorIsolationType) {
-    if (!_swift_task_isCurrentGlobalActorHook)
+    if (!_swift_task_isCurrentGlobalActorHook) {
+#if defined(__wasm__)
+      // FIXME: We don't currently support a concurrency model for WebAssembly,
+      // and the global actor hook isn't getting initialized due to the
+      // lack of __attribute__((constructor)) support. Therefore, we
+      // treat everything "as if" it were on the correct global actor.
+      return true;
+#else
       return false;
+#endif
+    }
 
     // Check whether we are running on this global actor.
     if (!_swift_task_isCurrentGlobalActorHook(