make SetunhandledExceptionFilter() thread-safe

reactos/lib/kernel32/except

diff -u -r1.18 -r1.19
--- except.c	10 Nov 2004 01:07:45 -0000	1.18
+++ except.c	12 Dec 2004 22:39:45 -0000	1.19
@@ -1,4 +1,4 @@

-/* $Id: except.c,v 1.18 2004/11/10 01:07:45 blight Exp $

+/* $Id: except.c,v 1.19 2004/12/12 22:39:45 weiden Exp $

  *
  * COPYRIGHT:       See COPYING in the top level directory
  * PROJECT:         ReactOS system libraries

@@ -46,10 +46,8 @@

     LPTOP_LEVEL_EXCEPTION_FILTER lpTopLevelExceptionFilter
     )
 {

-    LPTOP_LEVEL_EXCEPTION_FILTER OldTopLevelExceptionFilter =
-					 GlobalTopLevelExceptionFilter;
-    GlobalTopLevelExceptionFilter = lpTopLevelExceptionFilter;
-    return OldTopLevelExceptionFilter;

+    return InterlockedExchangePointer(&GlobalTopLevelExceptionFilter,
+                                      lpTopLevelExceptionFilter);

 }