Add std::filesystem support.

Test: ndk/run_tests.py
Bug: https://github.com/android/ndk/issues/609
Change-Id: Id01db3092d73eeecd38cd9292f6221c951979747
diff --git a/libcxx/Android.mk b/libcxx/Android.mk
index df90a4f..74f94cb 100644
--- a/libcxx/Android.mk
+++ b/libcxx/Android.mk
@@ -31,6 +31,9 @@
     condition_variable_destructor.cpp \
     debug.cpp \
     exception.cpp \
+    filesystem/directory_iterator.cpp \
+    filesystem/int128_builtins.cpp \
+    filesystem/operations.cpp \
     functional.cpp \
     future.cpp \
     hash.cpp \