Implement _Exit(3).

Change-Id: Ida6ac844cc87d38c9645b197dd8188bb73e27dbe
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index e597b2f..220c713 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -308,7 +308,7 @@
 
 int eventfd:eventfd2(unsigned int, int)  all
 
-void _exit:exit_group(int)  all
+void _exit|_Exit:exit_group(int)  all
 void __exit:exit(int)  all
 
 int futex(void*, int, int, void*, void*, int)  all