fdtrack: add wrapper for eventfd.

Bug: https://issuetracker.google.com/154450436
Test: bionic-unit-tests
Change-Id: I59013f0c4da0debbcc50269c64ae9db0cdc4eaa0
diff --git a/libc/Android.bp b/libc/Android.bp
index f73ae4a..ac961d4 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1022,8 +1022,7 @@
         "bionic/dup.cpp",
         "bionic/environ.cpp",
         "bionic/error.cpp",
-        "bionic/eventfd_read.cpp",
-        "bionic/eventfd_write.cpp",
+        "bionic/eventfd.cpp",
         "bionic/exec.cpp",
         "bionic/faccessat.cpp",
         "bionic/fchmod.cpp",