Make gensyscalls.py use the ALIAS_SYMBOL macro.

Change-Id: Ib94c0abb6fc85126ecc5ed3f1962b2b8b90b9952
diff --git a/libc/arch-x86/syscalls/_exit.S b/libc/arch-x86/syscalls/_exit.S
index 8528ee4..9945b35 100644
--- a/libc/arch-x86/syscalls/_exit.S
+++ b/libc/arch-x86/syscalls/_exit.S
@@ -20,5 +20,4 @@
     ret
 END(_exit)
 
-    .globl _Exit
-    .equ _Exit, _exit
+ALIAS_SYMBOL(_Exit, _exit)