Add preadv/pwritev.

Bug: http://b/12612572
Change-Id: I38ff2684d69bd0fe3f21b1d371b88fa60d5421cb
diff --git a/libc/libc.map b/libc/libc.map
index 9456920..fbceb83 100644
--- a/libc/libc.map
+++ b/libc/libc.map
@@ -1342,6 +1342,10 @@
     __write_chk;
     getgrgid_r;
     getgrnam_r;
+    preadv;
+    preadv64;
+    pwritev;
+    pwritev64;
     strchrnul;
 } LIBC;