misc/cgo/stdio: reenable tests

The build tags are necessary to keep "go build" in that directory
building only stdio.go, but we have to arrange for test/run.go to
treat them as satisfied.

Fixes #12625.

Change-Id: Iec0cb2fdc2c9b24a4e0530be25e940aa0cc9552e
Reviewed-on: https://go-review.googlesource.com/17454
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/life/main.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build ignore
+// +build test_run
 
 // Run the game of life in C using Go for parallelization.
 

misc/cgo/stdio/chain.go

@@ -4,16 +4,17 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build ignore
+// +build test_run
 
 // Pass numbers along a chain of threads.
 
 package main
 
 import (
-	"../stdio"
 	"runtime"
 	"strconv"
+
+	"../stdio"
 )
 
 const N = 10

misc/cgo/stdio/fib.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build ignore
+// +build test_run
 
 // Compute Fibonacci numbers with two goroutines
 // that pass integers back and forth.  No actual
@@ -14,9 +14,10 @@
 package main
 
 import (
-	"../stdio"
 	"runtime"
 	"strconv"
+
+	"../stdio"
 )
 
 func fibber(c, out chan int64, i int64) {

misc/cgo/stdio/hello.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build ignore
+// +build test_run
 
 package main
 

test/run.go

@@ -400,6 +400,10 @@ func (ctxt *context) match(name string) bool {
 		return true
 	}
 
+	if name == "test_run" {
+		return true
+	}
+
 	return false
 }