cmd/link: add missing error check in test

Change-Id: I54998f1b7daa8f8db7a2007b4eb86e9789c03656
GitHub-Last-Rev: 97667ead6f62dad2af0d6b1f78deccef16417044
GitHub-Pull-Request: golang/go#30006
Reviewed-on: https://go-review.googlesource.com/c/160430Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/link/linkbig_test.go

@@ -28,6 +28,9 @@ func TestLargeText(t *testing.T) {
 	var w bytes.Buffer
 	const FN = 4
 	tmpdir, err := ioutil.TempDir("", "bigtext")
+	if err != nil {
+		t.Fatalf("can't create temp directory: %v\n", err)
+	}
 
 	defer os.RemoveAll(tmpdir)