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/CMakeLists.txt

@@ -6,3 +6,12 @@ add_library(platform-posix OBJECT)
 target_sources(platform-posix PRIVATE ${SOURCES})
 #target_include_directories(platform-posix PUBLIC include/)
 target_link_libraries(platform-posix PUBLIC TactilityKernel)
+
+# Routes every pthread_attr_setstack() call to __wrap_pthread_attr_setstack() in source/pthread_stack_wrap.c,
+# which no-ops it. see that file for why.
+# --wrap is a GNU ld option; Apple's linker doesn't support it, so that file instead self-registers a dyld interpose
+# for this symbol on Apple, needing no link flag. PUBLIC so every consumer of this OBJECT library
+# (Tactility, and every test target that links platform-posix directly) gets it applied too.
+if (NOT APPLE)
+    target_link_options(platform-posix PUBLIC "-Wl,--wrap=pthread_attr_setstack")
+endif ()