goprotobuf: Update build tags to use unsafe (but faster) code on Managed VMs.
LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/91040044
diff --git a/proto/pointer_reflect.go b/proto/pointer_reflect.go
index 796bfc9..61141ba 100644
--- a/proto/pointer_reflect.go
+++ b/proto/pointer_reflect.go
@@ -29,7 +29,7 @@
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-// +build appengine
+// +build appengine,!appenginevm
// This file contains an implementation of proto field accesses using package reflect.
// It is slower than the code in pointer_unsafe.go but it avoids package unsafe and can