This is a pretty mechanical patch, that fixes one annoyance I had
when I started reading the gdbserver win32 support code.  There is an
opaque struct thread_info declared in server.h, and the win32-low.c
file implements a 'typedef struct win32_thread_info thread_info'.  I
find it confusing to have code like:

thread_rec (DWORD id, int get_context)
{
     struct thread_info *thread;
     thread_info *th;

I only noticed the types where unrelated after my first working
gdbserver/WinCE prototype was working :)

The attached patch should make the code clearer.