Expose ftello64.

Also add the missing test that would have caught this.

Bug: http://b/24807045
Change-Id: I756a4d825595b52396b15898e3f717156fd1ba2f
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 3a8f7d7..e2aede5 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1255,6 +1255,7 @@
     freeifaddrs;
     fseeko64;
     fsetpos64;
+    ftello64;
     funopen64;
     getgrgid_r;
     getgrnam_r;