Fixup Win32

Fixup Win32
- #undef start_env before re-#defining it
- change pp_specific pp_threadsv in global.sym
- re-build embed.h
- avoid HAVE_THREAD_INTERN - we don't and empty struct
  is a pain. If we did have it it would contain cached
  values of things we can only get at _IN_ the thread
  so new_struct_thread is wrong place to call it.
- add new macro SET_THREAD_SELF - we must (in main thread)
  define in win32thread.h, support in win32thread.c,
  test and call in perl.c

p4raw-id: //depot/ansiperl@237