fdtrack: add wrapper for socketpair.

Bug: https://issuetracker.google.com/154450436
Test: bionic-unit-tests
Change-Id: I8b25accf00dc01f6fab351f3ba612f6b0ff9d094
diff --git a/libc/Android.bp b/libc/Android.bp
index ac961d4..d5d0afb 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1113,6 +1113,7 @@
         "bionic/signal.cpp",
         "bionic/sigprocmask.cpp",
         "bionic/sleep.cpp",
+        "bionic/socketpair.cpp",
         "bionic/spawn.cpp",
         "bionic/stat.cpp",
         "bionic/stdlib_l.cpp",