chmod +x before running a gtest on the target

otherwise binaries written by flashing userdata.img cannot be run.

Change-Id: I495ca3cde4e5d7cbdf6b535b5d38345da4846e90
diff --git a/build/Android.gtest.mk b/build/Android.gtest.mk
index 5a9f613..9f75115 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -100,6 +100,7 @@
 $$(art_gtest_target): $$(art_gtest_exe) test-art-target-sync
 	adb shell touch $(ART_TEST_DIR)/$$@
 	adb shell rm $(ART_TEST_DIR)/$$@
+	adb shell chmod 755 $(ART_NATIVETEST_DIR)/$$(notdir $$<)
 	adb shell sh -c "$(ART_NATIVETEST_DIR)/$$(notdir $$<) && touch $(ART_TEST_DIR)/$$@"
 	$(hide) (adb pull $(ART_TEST_DIR)/$$@ /tmp/ && echo $$@ PASSED) || (echo $$@ FAILED && exit 1)
 	$(hide) rm /tmp/$$@