atexit doesn't take a _onexit_t parameter.

dlls/msvcrt/exit.c

@@ -191,12 +191,13 @@ void MSVCRT_exit(int exitcode)
 /*********************************************************************
  *		atexit (MSVCRT.@)
  */
-int MSVCRT_atexit(_onexit_t func)
+int MSVCRT_atexit(void (*func)(void))
 {
   TRACE("(%p)\n", func);
-  return _onexit(func) == func ? 0 : -1;
+  return _onexit((_onexit_t)func) == (_onexit_t)func ? 0 : -1;
 }
 
+
 /*********************************************************************
  *		_purecall (MSVCRT.@)
  */

include/msvcrt/stdlib.h

@@ -138,7 +138,7 @@ char*       _ultoa(unsigned long,char*,int);
 void        MSVCRT(_exit)(int);
 void        MSVCRT(abort)();
 int         MSVCRT(abs)(int);
-int         MSVCRT(atexit)(_onexit_t);
+int         MSVCRT(atexit)(void (*)(void));
 double      MSVCRT(atof)(const char*);
 int         MSVCRT(atoi)(const char*);
 long        MSVCRT(atol)(const char*);