Enable cross compile to android from mac.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index b1b23b0220ff355a6183c05589c795d1805cc1e9..4b8121b5ed17a8b98add2ea4e76cecc15f522907 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1572,9 +1572,11 @@ template("unittest_apk") {
       deps += invoker.deps
     }
     datadeps = [
-      "//tools/android/forwarder2",
       "//tools/android/md5sum",
     ]
+    if (host_os == "linux") {
+      datadeps += [ "//tools/android/forwarder2" ]
+    }
     if (defined(invoker.datadeps)) {
       datadeps += invoker.datadeps
     }