atexit has no return type and gcc grumbles.

Notes:
Fri Mar 14 00:07:43 EDT 2008 geoff
    gcc whinges about all sorts of things it has no business
    whinging about.  a function with no declared return type
    returns int; it's always been that way.  if stallman doesn't
    like it, just turn off (or down) his warnings.


Reference: /n/sources/patch/sorry/atexit-retval
Date: Thu Mar 13 13:39:22 CET 2008
Signed-off-by: steve@quintile.net
Reviewed-by: geoff

--- /sys/src/libc/port/atexit.c	Thu Mar 13 13:39:06 2008
+++ /sys/src/libc/port/atexit.c	Thu Mar 13 13:39:03 2008
@@ -12,6 +12,7 @@
 static Lock onexlock;
 Onex onex[NEXIT];
 
+int
 atexit(void (*f)(void))
 {
 	int i;