fdtrack: add wrapper for eventfd.

Bug: https://issuetracker.google.com/154450436
Test: bionic-unit-tests
Change-Id: I59013f0c4da0debbcc50269c64ae9db0cdc4eaa0
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index e8445fd..f235bc8 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -312,7 +312,7 @@
 int epoll_ctl(int, int op, int, struct epoll_event*)  all
 int __epoll_pwait:epoll_pwait(int, struct epoll_event*, int, int, const sigset64_t*, size_t)  all
 
-int eventfd:eventfd2(unsigned int, int)  all
+int __eventfd:eventfd2(unsigned int, int)  all
 
 void _exit|_Exit:exit_group(int)  all
 void __exit:exit(int)  all