New file msvcrt/excpt.h. Move some stuff out of winnt.h into it.

diff --git a/include/windows.h b/include/windows.h
index a041926..575dec7 100644
--- a/include/windows.h
+++ b/include/windows.h
@@ -10,7 +10,7 @@
 #else /* RC_INVOKED && !NOWINRES */
 
 /* All the basic includes */
-/* #include "excpt.h" */
+#include "msvcrt/excpt.h"
 #include "windef.h"
 #include "winbase.h"
 #include "wingdi.h"