go/build: exclude cgo test from arm

go/build: include command output in error values
go/build: add syslist.go to .hgignore

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4550118

.hgignore

@@ -42,6 +42,7 @@ src/cmd/gc/yerr.h
 src/cmd/goinstall/syslist.go
 src/pkg/Make.deps
 src/pkg/exp/ogle/ogle
+src/pkg/go/build/syslist.go
 src/pkg/os/signal/unix.go
 src/pkg/runtime/*/asm.h
 src/pkg/runtime/goc2c

src/pkg/go/build/build.go

@@ -6,6 +6,7 @@
 package build
 
 import (
+	"bytes"
 	"exec"
 	"fmt"
 	"os"
@@ -79,8 +80,11 @@ func (c *Cmd) String() string {
 }
 
 func (c *Cmd) Run(dir string) os.Error {
+	out := new(bytes.Buffer)
 	cmd := exec.Command(c.Args[0], c.Args[1:]...)
 	cmd.Dir = dir
+	cmd.Stdout = out
+	cmd.Stderr = out
 	if c.Stdout != "" {
 		f, err := os.Create(filepath.Join(dir, c.Stdout))
 		if err != nil {
@@ -90,7 +94,7 @@ func (c *Cmd) Run(dir string) os.Error {
 		cmd.Stdout = f
 	}
 	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("command %q: %v", c, err)
+		return fmt.Errorf("command %q: %v\n%v", c, err, out)
 	}
 	return nil
 }

src/pkg/go/build/build_test.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strings"
 	"testing"
 )
 
@@ -24,6 +25,10 @@ func TestBuild(t *testing.T) {
 		t.Fatal(err)
 	}
 	for _, d := range buildDirs {
+		if runtime.GOARCH == "arm" && strings.Contains(d, "/cgo") {
+			// no cgo for arm, yet.
+			continue
+		}
 		dir := filepath.Join(runtime.GOROOT(), "src", d)
 		testBuild(t, dir, out)
 	}