cmd/go: leave directory before removing it in TestSharedLibName

Fixes #15124

Change-Id: I55fe4c2957370f3fb417c3df54f99fb085a5dada
Reviewed-on: https://go-review.googlesource.com/21522Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/pkg_test.go

@@ -161,9 +161,12 @@ func TestSharedLibName(t *testing.T) {
 				}
 				oldGopath := buildContext.GOPATH
 				defer func() {
-					os.RemoveAll(tmpGopath)
 					buildContext.GOPATH = oldGopath
 					os.Chdir(cwd)
+					err := os.RemoveAll(tmpGopath)
+					if err != nil {
+						t.Error(err)
+					}
 				}()
 				root := filepath.Join(tmpGopath, "src", data.rootedAt)
 				err = os.MkdirAll(root, 0755)