I'm very pleased to report that, thanks to the hard work of Chris Manghane, the Go frontend no longer includes any header files from GCC. This means that global changes to the GCC middle-end no longer need to touch any files in gcc/go/gofrontend. Instead, they will only need to modify files in gcc/go, files that are under the GPL and can be maintained using the usual GCC processes.
This finally fulfills a promise I made when the Go frontend was added to GCC. Ian
