Annotate callback functions with __stdcall on Windows

Fixes crash on exit on Windows x86.

Headers/GNUstepBase/GSConfig.h.in

@@ -337,6 +337,13 @@ typedef	struct {
 #  undef  BOOL
 #endif
 
+/* Used to annotate callback functions with __stdcall on Windows. */
+#if defined(_WIN32)
+#define GS_WINAPI WINAPI
+#else
+#define GS_WINAPI
+#endif
+
 /* Include the blocks runtime header if it's available (It shouldn't matter
  * that this doesn't work on compilers that don't support __has_include(),
  * because they also don't support blocks).

Source/GSFFIInvocation.m

@@ -256,10 +256,18 @@ static id gs_objc_proxy_lookup(id receiver, SEL op)
 }
 #endif
 
+#ifdef __GNUSTEP_RUNTIME__
+static void GS_WINAPI
+exitedThread(void *slot)
+{
+  free(slot);
+}
+#endif
+
 + (void) load
 {
 #ifdef __GNUSTEP_RUNTIME__
-  GS_THREAD_KEY_INIT(thread_slot_key, free);
+  GS_THREAD_KEY_INIT(thread_slot_key, exitedThread);
   __objc_msg_forward3 = gs_objc_msg_forward3;
   __objc_msg_forward2 = gs_objc_msg_forward2;
   objc_proxy_lookup = gs_objc_proxy_lookup;

Source/NSThread.m

@@ -642,7 +642,8 @@ unregisterActiveThread(NSThread *thread);
  * we must not call into NSAutoreleasePool unless the NSThread object can still
  * be found using GSCurrentThread()
  */
-static void exitedThread(void *thread)
+static void GS_WINAPI
+exitedThread(void *thread)
 {
   if (thread != defaultThread)
     {