cmd/go: prohibit C sources files unless using cgo

Those C files would have been compiled with 6c.
It's close to impossible to use C correctly anymore,
and the C compilers are going away eventually.
Make them unavailable now.

go1.4.txt change in CL 145890046

LGTM=iant
R=iant
CC=golang-codereviews, r
https://codereview.appspot.com/149720043

4 files changed, 1 insertions, 61 deletions

diff --git a/misc/cgo/test/backdoor/backdoor.go b/misc/cgo/test/backdoor/backdoor.go
index 7398772bd..3a973494b 100644
--- a/misc/cgo/test/backdoor/backdoor.go
+++ b/misc/cgo/test/backdoor/backdoor.go
@@ -4,5 +4,4 @@
 
 package backdoor
 
-func LockedOSThread() bool // in runtime.c
-func Issue7695(x1, x2, x3, x4, x5, x6, x7, x8 uintptr)
+func LockedOSThread() bool // in thunk.s
diff --git a/misc/cgo/test/backdoor/backdoor_gccgo.go b/misc/cgo/test/backdoor/backdoor_gccgo.go
deleted file mode 100644
index 514f76ec5..000000000
--- a/misc/cgo/test/backdoor/backdoor_gccgo.go
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2014 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// This is the gccgo version of the stub in runtime.c.
-
-// +build gccgo
-
-package backdoor
-
-func Issue7695(x1, x2, x3, x4, x5, x6, x7, x8 uintptr) {}
diff --git a/misc/cgo/test/backdoor/runtime.c b/misc/cgo/test/backdoor/runtime.c
deleted file mode 100644
index 87ee44eb6..000000000
--- a/misc/cgo/test/backdoor/runtime.c
+++ /dev/null
@@ -1,18 +0,0 @@
-// Copyright 2011 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Expose some runtime functions for testing.
-// Must be in a non-cgo-using package so that
-// the go command compiles this file with 6c, not gcc.
-
-// +build gc
-
-typedef char bool;
-
-// This is what a cgo-compiled stub declaration looks like.
-void
-·Issue7695(struct{void *y[8*sizeof(void*)];}p)
-{
-	USED(p);
-}
diff --git a/misc/cgo/test/issue7695_test.go b/misc/cgo/test/issue7695_test.go
deleted file mode 100644
index de2fc03d4..000000000
--- a/misc/cgo/test/issue7695_test.go
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2014 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build ignore
-// This test depends on running C code on Go stacks. Not allowed anymore.
-
-// Demo of deferred C function with untrue prototype
-// breaking stack copying. See golang.org/issue/7695.
-
-package cgotest
-
-import (
-	"testing"
-
-	"./backdoor"
-)
-
-func TestIssue7695(t *testing.T) {
-	defer backdoor.Issue7695(1, 0, 2, 0, 0, 3, 0, 4)
-	recurse(100)
-}
-
-func recurse(n int) {
-	var x [128]int
-	n += x[0]
-	if n > 0 {
-		recurse(n - 1)
-	}
-}