Make gensyscalls.py use the ALIAS_SYMBOL macro.

Change-Id: Ib94c0abb6fc85126ecc5ed3f1962b2b8b90b9952
diff --git a/libc/arch-arm64/syscalls/pwrite64.S b/libc/arch-arm64/syscalls/pwrite64.S
index 6970954..1599c14 100644
--- a/libc/arch-arm64/syscalls/pwrite64.S
+++ b/libc/arch-arm64/syscalls/pwrite64.S
@@ -13,5 +13,4 @@
     ret
 END(pwrite64)
 
-    .globl pwrite
-    .equ pwrite, pwrite64
+ALIAS_SYMBOL(pwrite, pwrite64)