_Exit(): add weak alias to _exit() for C99

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/sysdeps/linux/common/_exit.c

@@ -21,3 +21,4 @@ void attribute_noreturn _exit(int status)
 		INLINE_SYSCALL(exit, 1, status);
 }
 libc_hidden_def(_exit)
+weak_alias(_exit,_Exit)