Ignore .cxx

Summary:
Seems to be a new thing from the Android Build system
and it's quite annoying.

Reviewed By: jknoxville

Differential Revision: D17163339

fbshipit-source-id: 938264d301e7546a4a6e3276e91184ab5498a833

.gitignore

@@ -23,6 +23,7 @@ local.properties
 **/.classpath
 android/*/bin/**/*.class
 libs/*/bin/**/*.class
+.cxx
 
 # Mac OS X
 *.DS_Store