Add trivial no-op <nl_types.h>.

Needed to build OpenMP.

Bug: http://b/27617302
Change-Id: Iac15c84ead6f5d5274cfdb2d6d4a4ec0072244bb
diff --git a/libc/Android.mk b/libc/Android.mk
index c74c237..fa392d1 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -145,6 +145,7 @@
     bionic/NetdClientDispatch.cpp \
     bionic/net_if.cpp \
     bionic/netinet_in.cpp \
+    bionic/nl_types.cpp \
     bionic/open.cpp \
     bionic/pathconf.cpp \
     bionic/pause.cpp \