gc: do not build builtin.c automatically; use golden copy instead.

R=r
CC=golang-dev
https://golang.org/cl/190104

src/cmd/gc/Makefile

@@ -54,9 +54,8 @@ y.tab.h: $(YFILES)
 y.tab.c: y.tab.h
 	test -f y.tab.c && touch y.tab.c
 
-builtin.c:	runtime.go unsafe.go mkbuiltin1.c mkbuiltin
-	./mkbuiltin || \
-	(echo 'mkbuiltin failed; using bootstrap copy of builtin.c'; cp builtin.c.boot builtin.c)
+builtin.c: builtin.c.boot
+	cp builtin.c.boot builtin.c
 
 subr.$O: opnames.h
 

src/cmd/gc/mkbuiltin

@@ -3,6 +3,11 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
+# Generate builtin.c and builtin.c.boot from $* (runtime.go and unsafe.go).
+# Run this after changing runtime.go and unsafe.go
+# or after changing the export metadata format in the compiler.
+# Either way, you need to have a working compiler binary first.
+
 set -e
 
 GOBIN="${GOBIN:-$HOME/bin}"
@@ -22,19 +27,7 @@ do
 done
 
 # If _builtin.c has changed vs builtin.c.boot,
-# check in the new change if being run by
-# one of the people who tends to work on
-# the compiler.  This makes sure that changes
-# don't get forgotten, without causing problems
-# in end user Go repositories.
-case "$USER" in
-ken | r | rsc)
-	if ! cmp _builtin.c builtin.c.boot >/dev/null 2>/dev/null
-	then
-		PATH=$PATH:/usr/local/bin	# find p4 on OS X
-		p4 open builtin.c.boot >/dev/null 2>/dev/null || true	# if p4 is missing, so be it
-		cp _builtin.c builtin.c.boot
-	fi
-esac
+# check in the new change.
+cmp -s _builtin.c builtin.c.boot || cp _builtin.c builtin.c.boot
 
 mv _builtin.c builtin.c

src/cmd/gc/runtime.go

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// NOTE: If you change this file you must run "./mkbuiltin"
+// to update builtin.c.boot.  This is not done automatically
+// to avoid depending on having a working compiler binary.
+
 package PACKAGE
 
 // emitted by compiler, not referred to by go programs

src/cmd/gc/unsafe.go

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// NOTE: If you change this file you must run "./mkbuiltin"
+// to update builtin.c.boot.  This is not done automatically
+// to avoid depending on having a working compiler binary.
+
 package PACKAGE
 
 type Pointer *any