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.

Platforms/platform-posix/source/pthread_stack_wrap.c

@@ -2,20 +2,15 @@
 #include <stddef.h>
 
 /**
- * Linked in with -Wl,--wrap=pthread_attr_setstack (see Tactility/CMakeLists.txt).
+ * FreeRTOS's POSIX port hands every task a stack carved from its own heap (pvPortMalloc) via this call.
+ * pthread_attr_setstack requires page alignment that pvPortMalloc doesn't guarantee.
+ * When it succeeds anyway, the task's real pthread stack ends up living inside that small FreeRTOS heap region,
+ * where a thread doing heavier stack work (e.g. Mesa GL shader compilation) can silently corrupt adjacent heap_4 objects.
+ * No-op'ing the call instead leaves every task's pthread_attr_t at its pthread_attr_init() default,
+ * so pthread_create() gives it a real, properly sized stack.
  *
- * FreeRTOS's POSIX port (Libraries/FreeRTOS-Kernel/portable/ThirdParty/GCC/Posix/port.c)
- * hands every task a stack carved out of its own heap (pvPortMalloc) via this call.
- * pthread_attr_setstack requires page alignment, which pvPortMalloc doesn't guarantee;
- * when it happens to succeed anyway (allocator alignment can vary run to run), the
- * task's real pthread stack ends up living inside that small FreeRTOS heap region -
- * fine for typical embedded task code, but a desktop GL driver doing on-the-fly shader
- * compilation on that thread (e.g. Mesa on first frame present) can overflow it and
- * silently corrupt adjacent heap_4 objects.
- *
- * Wrapping the call out entirely (rather than patching the vendored port.c) leaves every
- * task's pthread_attr_t at its pthread_attr_init() default, so pthread_create() always
- * gives it a real, properly allocated default-size stack instead.
+ * Linked via -Wl,--wrap=pthread_attr_setstack (this module's own CMakeLists.txt) on non-Apple
+ * platforms; reused as a dyld interpose target below on Apple platforms, whose linker lacks --wrap.
  */
 int __wrap_pthread_attr_setstack(pthread_attr_t* attr, void* stackaddr, size_t stacksize) {
     (void)attr;
@@ -23,3 +18,17 @@ int __wrap_pthread_attr_setstack(pthread_attr_t* attr, void* stackaddr, size_t s
     (void)stacksize;
     return 0;
 }
+
+#ifdef __APPLE__
+
+// <mach-o/dyld-interposing.h> isn't a public SDK header (it ships with dyld's own source, not
+// Xcode/Command Line Tools), so this reimplements its DYLD_INTERPOSE macro locally.
+#define TT_DYLD_INTERPOSE(replacement, replacee) \
+    __attribute__((used)) static struct { const void* replacement; const void* replacee; } \
+        tt_interpose_##replacee __attribute__((section("__DATA,__interpose"))) = { \
+            (const void*)(unsigned long)&(replacement), (const void*)(unsigned long)&(replacee) \
+        };
+
+TT_DYLD_INTERPOSE(__wrap_pthread_attr_setstack, pthread_attr_setstack)
+
+#endif