cmd/go: fix list -compiled of package with only tests

Fixes #27097.

Change-Id: I6aa48a1c58a21fd320b0e9dcd1f86c90172f0182
Reviewed-on: https://go-review.googlesource.com/130139
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/list/list.go

@@ -510,7 +510,9 @@ func runList(cmd *base.Command, args []string) {
 		a := &work.Action{}
 		// TODO: Use pkgsFilter?
 		for _, p := range pkgs {
-			a.Deps = append(a.Deps, b.AutoAction(work.ModeInstall, work.ModeInstall, p))
+			if len(p.GoFiles)+len(p.CgoFiles) > 0 {
+				a.Deps = append(a.Deps, b.AutoAction(work.ModeInstall, work.ModeInstall, p))
+			}
 		}
 		b.Do(a)
 	}

src/cmd/go/testdata/script/mod_list_test.txt

+env GO111MODULE=on
+
+# go list -compiled -test must handle test-only packages
+# golang.org/issue/27097.
+go list -compiled -test
+stdout '^m$'
+stdout '^m\.test$'
+stdout '^m \[m\.test\]$'
+
+-- go.mod --
+module m
+
+-- x_test.go --
+package x
+import "testing"
+func Test(t *testing.T) {}