Share windows_thread_info between gdb and gdbserver

This introduces a new file, nat/windows-nat.h, which holds the
definition of windows_thread_info.  This is now shared between gdb and
gdbserver.

Note that the two implementations different slightly.  gdb had a
couple of fields ("name" and "reload_context") that gdbserver did not;
while gdbserver had one field ("base_context") that gdb did not, plus
better comments.  The new file preserves all the fields, and the
comments.

gdb/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* windows-nat.c (struct windows_thread_info): Remove.
	* nat/windows-nat.h: New file.

gdbserver/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* win32-low.h (struct windows_thread_info): Remove.

gdbserver/win32-low.h

@@ -20,6 +20,7 @@
 #define GDBSERVER_WIN32_LOW_H
 
 #include <windows.h>
+#include "nat/windows-nat.h"
 
 struct target_desc;
 
@@ -27,35 +28,6 @@ struct target_desc;
    Windows ports support neither bi-arch nor multi-process.  */
 extern const struct target_desc *win32_tdesc;
 
-/* Thread information structure used to track extra information about
-   each thread.  */
-struct windows_thread_info
-{
-  /* The Win32 thread identifier.  */
-  DWORD tid;
-
-  /* The handle to the thread.  */
-  HANDLE h;
-
-  /* Thread Information Block address.  */
-  CORE_ADDR thread_local_base;
-
-  /* Non zero if SuspendThread was called on this thread.  */
-  int suspended;
-
-#ifdef _WIN32_WCE
-  /* The context as retrieved right after suspending the thread. */
-  CONTEXT base_context;
-#endif
-
-  /* The context of the thread, including any manipulations.  */
-  CONTEXT context;
-
-  /* Whether debug registers changed since we last set CONTEXT back to
-     the thread.  */
-  int debug_registers_changed;
-};
-
 struct win32_target_ops
 {
   /* Architecture-specific setup.  */