Fortify ppoll64.

I've deliberately not bothered with the GCC implementation because we'll
have removed GCC from the NDK before anyone gets to use this.

Bug: http://b/72493232
Test: ran tests
Change-Id: Icfc2a3b214739ab53aa41bacacc11b5c67498fb4
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 85c9a58..b787ea5 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -115,6 +115,7 @@
     __poll_chk; # introduced=23
     __ppoll; # arm x86 mips introduced=21
     __ppoll_chk; # introduced=23
+    __ppoll64_chk; # introduced=28
     __pread64_chk; # introduced=23
     __pread_chk; # introduced=23
     __progname; # var