Refactor SDL/FreeRTOS implementation to support macOS simulator properly (#653)

- Run SDL from main() and place FreeRTOS in separate thread. This fixes macOS support.
- Updated GitHub Actions to publish macOS simulator build for testing, updated amd64 to x86_64 for consistent naming.

Devices/simulator/Source/Simulator.h

@@ -1,6 +1,11 @@
 #pragma once
 
 #include "Main.h"
+#include "drivers/sdl_bridge.h"
+
+#include <csignal>
+#include <pthread.h>
+#include <thread>
 
 namespace simulator {
     /** Set the function pointer of the real app_main() */
@@ -14,8 +19,23 @@ void app_main(); // ESP-IDF's main function, implemented in the application
 }
 
 int main() {
-    // Actual main function that passes on app_main() (to be executed in a FreeRTOS task) and bootstraps FreeRTOS
+    // The FreeRTOS POSIX port arms a process-wide SIGALRM timer for its tick and expects every one
+    // of its task pthreads to have all signals but SIGINT blocked.
+    // (see prvSetupSignalsAndSchedulerPolicy() in FreeRTOS-Kernel's Posix port.c)
+    // A signal-generated SIGALRM can land on any thread in the process that doesn't block it.
+    // This thread stays a plain OS thread (running the SDL loop below, never a FreeRTOS task),
+    // so without this it's eligible to catch a tick SIGALRM and freeze inside the scheduler's handler.
+    // Block the same set here, before anything else, so it never can.
+    sigset_t all_signals_except_sigint;
+    sigfillset(&all_signals_except_sigint);
+    sigdelset(&all_signals_except_sigint, SIGINT);
+    pthread_sigmask(SIG_SETMASK, &all_signals_except_sigint, nullptr);
+
+    // FreeRTOS and app_main() run on a separate thread: macOS requires SDL/Cocoa window creation,
+    // event pumping and rendering to happen on the real OS main thread, which sdl_bridge_run_main_loop()
+    // below takes over. freertosMain() never returns, so this thread is detached rather than joined.
     simulator::setMain(app_main);
-    simulator::freertosMain();
+    std::thread(simulator::freertosMain).detach();
+    sdl_bridge_run_main_loop();
     return 0;
 }