#include "go.h" (or "gg.h")
becomes
#include <u.h>
#include <libc.h>
#include "go.h"
so that go.y can #include <stdio.h>
after <u.h> but before "go.h".
This is necessary on Plan 9.
R=ken2
CC=golang-dev
https://golang.org/cl/4971041
For now it's switch-on-and-offable with -s, and the effects can be inspected
with -m. Defaults are the old codepaths.
R=rsc
CC=golang-dev
https://golang.org/cl/4634073