sharedspice.c, use GetCurrentThreadId() instead of GetTreadID()

Thanks to Thomas Uhle for this patch, see
  http://sourceforge.net/p/ngspice/patches/26/
  #26 GetThreadId() missing in older Win32 API, proposing to use GetCurrentThreadId() instead

src/sharedspice.c

@@ -76,7 +76,7 @@ typedef SRWLOCK mutexType;
 typedef CRITICAL_SECTION mutexType;
 #endif
 #define thread_self() GetCurrentThread()
-#define threadid_self() GetThreadId(GetCurrentThread())
+#define threadid_self() GetCurrentThreadId()
 typedef HANDLE threadId_t;
 #define WIN_THREADS
 #define THREADS