cmd: fix unused errors reported by ineffassign

Updates golang/go#35136

Change-Id: I36d26089d29933e363d9fa50f3174530b698450e
Reviewed-on: https://go-review.googlesource.com/c/go/+/731040
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Florian Lehner <lehner.florian86@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/internal/bootstrap_test/overlaydir_test.go

@@ -43,6 +43,9 @@ func overlayDir(dstRoot, srcRoot string) error {
 		dstPath := filepath.Join(dstRoot, suffix)
 
 		info, err := entry.Info()
+		if err != nil {
+			return err
+		}
 		perm := info.Mode() & os.ModePerm
 		if info.Mode()&os.ModeSymlink != 0 {
 			info, err = os.Stat(srcPath)

src/cmd/link/link_test.go

@@ -869,6 +869,9 @@ func TestFuncAlignOption(t *testing.T) {
 			"_main.bar": false,
 			"_main.baz": false}
 		syms, err := f.Symbols()
+		if err != nil {
+			t.Errorf("failed to get symbols with err %v", err)
+		}
 		for _, s := range syms {
 			fn := s.Name
 			if _, ok := fname[fn]; !ok {