misc/cgo/test: skip TestCrossPackageTests on Android

This test currently fails in the Android builders, with the message
	pkg_test.go:64: go test -short: exec: "go": executable file not found in $PATH
(https://build.golang.org/log/39ec0da5bfb7793359e199cc8e358ca5a8257840)

I was not able to test this change, because I can't get 'gomote
create' to return an instance of anything Android. However, I will
watch the build dashboard after submitting to verify that the fix
works.

Updates #30228

Android appears to lack a 'go' command in the.

Change-Id: Ieacac7f50d19e2cfef2f5d60e79a159e55b5cfa8
Reviewed-on: https://go-review.googlesource.com/c/164097
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Elias Naur <mail@eliasnaur.com>

misc/cgo/test/pkg_test.go

@@ -27,7 +27,10 @@ import (
 // this shim and move the tests currently located in testdata back into the
 // parent directory.
 func TestCrossPackageTests(t *testing.T) {
-	if runtime.GOOS == "darwin" {
+	switch runtime.GOOS {
+	case "android":
+		t.Skip("Can't exec cmd/go subprocess on Android.")
+	case "darwin":
 		switch runtime.GOARCH {
 		case "arm", "arm64":
 			t.Skip("Can't exec cmd/go subprocess on iOS.")