issue 9656: cmd/pack TestLargeDefs uses too much disk space

gistfile1.diff

diff --git a/src/cmd/pack/pack.go b/src/cmd/pack/pack.go
index f65ae0c..90152af 100644
--- a/src/cmd/pack/pack.go
+++ b/src/cmd/pack/pack.go
@@ -426,20 +426,18 @@ func readPkgdef(file string) (data []byte, err error) {
 	// Read from file, collecting header for __.PKGDEF.
 	// The header is from the beginning of the file until a line
 	// containing just "!". The first line must begin with "go object ".
-	rbuf := bufio.NewReader(f)
 	var wbuf bytes.Buffer
-	for {
-		line, err := rbuf.ReadBytes('\n')
-		if err != nil {
-			return nil, err
-		}
-		if wbuf.Len() == 0 && !bytes.HasPrefix(line, []byte("go object ")) {
+	scan := bufio.NewScanner(f)
+	for scan.Scan() {
+		line := scan.Text()
+		if wbuf.Len() == 0 && !strings.HasPrefix(line, ("go object ")) {
 			return nil, errors.New("not a Go object file")
 		}
-		if bytes.Equal(line, []byte("!\n")) {
+		if line == "!" {
 			break
 		}
-		wbuf.Write(line)
+		wbuf.WriteString(line)
+		wbuf.WriteString("\n")
 	}
 	return wbuf.Bytes(), nil
 }
diff --git a/src/cmd/pack/pack_test.go b/src/cmd/pack/pack_test.go
index cf6121f..0c58d62 100644
--- a/src/cmd/pack/pack_test.go
+++ b/src/cmd/pack/pack_test.go
@@ -258,7 +258,7 @@ func TestLargeDefs(t *testing.T) {
 	}
 
 	printf("package large\n\ntype T struct {\n")
-	for i := 0; i < 10000; i++ {
+	for i := 0; i < 1000; i++ {
 		printf("f%d int `tag:\"", i)
 		for j := 0; j < 100; j++ {
 			printf("t%d=%d,", j, j)