Add preadv/pwritev.

Bug: http://b/12612572
Change-Id: I38ff2684d69bd0fe3f21b1d371b88fa60d5421cb
diff --git a/libc/arch-arm64/syscalls/preadv.S b/libc/arch-arm64/syscalls/preadv.S
new file mode 100644
index 0000000..cb8300d
--- /dev/null
+++ b/libc/arch-arm64/syscalls/preadv.S
@@ -0,0 +1,16 @@
+/* Generated by gensyscalls.py. Do not edit. */
+
+#include <private/bionic_asm.h>
+
+ENTRY(preadv)
+    mov     x8, __NR_preadv
+    svc     #0
+
+    cmn     x0, #(MAX_ERRNO + 1)
+    cneg    x0, x0, hi
+    b.hi    __set_errno_internal
+
+    ret
+END(preadv)
+
+ALIAS_SYMBOL(preadv64, preadv)