add fortified implementations of send/sendto

Bug: None
Test: Bullhead builds+boots; CtsBionicTestCases passes.
Change-Id: I2f137a100f679f7f2145d84b2f29ddd3e96a36ae
diff --git a/libc/libc.x86_64.map b/libc/libc.x86_64.map
index f88c284..061c8ba 100644
--- a/libc/libc.x86_64.map
+++ b/libc/libc.x86_64.map
@@ -1188,6 +1188,7 @@
 
 LIBC_O {
   global:
+    __sendto_chk; # future
     __system_property_read_callback; # future
     catclose; # future
     catgets; # future