Add trivial no-op <nl_types.h>.

Needed to build OpenMP.

Bug: http://b/27617302
Change-Id: Iac15c84ead6f5d5274cfdb2d6d4a4ec0072244bb
diff --git a/libc/Android.bp b/libc/Android.bp
index 5568760..3ec5e96 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -1317,6 +1317,7 @@
         "bionic/NetdClientDispatch.cpp",
         "bionic/net_if.cpp",
         "bionic/netinet_in.cpp",
+        "bionic/nl_types.cpp",
         "bionic/open.cpp",
         "bionic/pathconf.cpp",
         "bionic/pause.cpp",