Define internal FB macro for OSS builds.

Reviewed By: hramos

Differential Revision: D6626785

fbshipit-source-id: bb7c89499bc7c72e24dabd82899c3d9c49874101

ReactAndroid/DEFS

@@ -111,3 +111,7 @@ def rn_robolectric_test(name, srcs, vm_args = None, *args, **kwargs):
 original_cxx_library = cxx_library
 def cxx_library(allow_jni_merging=None, **kwargs):
     original_cxx_library(**kwargs)
+
+
+def fb_xplat_cxx_library(*args, **kwargs):
+    cxx_library(*args, **kwargs)