[check-system] Make memfs-cpp check-system clean

    ERROR at //zircon/system/ulib/memfs/memfs.cc:10:11: Include not allowed.
    #include <lib/memfs/memfs.h>
              ^----------------
    It is not in any dependency of
      //zircon/system/ulib/memfs:memfs-cpp
    The include file is in the target(s):
      //zircon/system/ulib/memfs:memfs
    which should somehow be reachable.

Bug: 55166
Change-Id: Id522e1ca7e5907a732228d892532fed282ae4965
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/404976
Commit-Queue: Scott Graham <scottmg@google.com>
Reviewed-by: Rasha Eqbal <rashaeqbal@google.com>
diff --git a/zircon/system/ulib/memfs/BUILD.gn b/zircon/system/ulib/memfs/BUILD.gn
index 233af7eb..47e0b19 100644
--- a/zircon/system/ulib/memfs/BUILD.gn
+++ b/zircon/system/ulib/memfs/BUILD.gn
@@ -25,6 +25,7 @@
     "directory.cc",
     "dnode.cc",
     "file.cc",
+    "include/lib/memfs/memfs.h",
     "memfs.cc",
     "vmo.cc",
   ]