stopped rebuilding everything when generated code doesn't change
diff --git a/aos/build/queues/print_field.rb b/aos/build/queues/print_field.rb
index 7a9fbb4..a86140f 100644
--- a/aos/build/queues/print_field.rb
+++ b/aos/build/queues/print_field.rb
@@ -4,7 +4,7 @@
["uint#{size}_t", "int#{size}_t"]
end.flatten + ['bool', 'float', 'char', 'double']
-File.open(ARGV[0], 'w') do |output|
+WriteIffChanged.open(ARGV[0]) do |output|
output.puts <<END
// This file is generated by #{File.expand_path(__FILE__)}.
// DO NOT EDIT BY HAND!