Crash at startup in Cygwin w32 build on emacs-25 branch

[Andy Moreton <andrewjmoreton@gmail.com>]

The changes in commit d696d62fea48 cause an instant crash at startup for
the cygwin w32 build, as the main Windows thread ID is not initialized.
The following patch fixes it.

diff --git a/src/emacs.c b/src/emacs.c
index c411da6a5da8..48ff20a11ce4 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -760,11 +760,11 @@ main (int argc, char **argv)
      to have non-stub implementations of APIs we need to convert file
      names between UTF-8 and the system's ANSI codepage.  */
   maybe_load_unicows_dll ();
+#endif
   /* This has to be done before module_init is called below, so that
      the latter could use the thread ID of the main thread.  */
   w32_init_main_thread ();
 #endif
-#endif

 #ifdef RUN_TIME_REMAP
   if (initialized)