- signal_alloc_thread() and signal_free_thread() mostly match signal_i386.c, but with the difference that first thread’s FS needs to be allocated in signal_init_process(). signal_alloc_thread() is called too early before the Wow TEB is allocated.
- The LDT code is copied from signal_i386.c. Would it be worthwhile to move that into a common file?
-- v3: ntdll: Set up 32-bit segments to support Wow64 on macOS 10.15+. ntdll: Store Wow64 FS selector in thread_data.