Enable '-h' command line option for printing 971-specific gtest help.

Change-Id: If857a1c2cd2e358cde4e7824f7a9bc497b11cc7b
diff --git a/aos/externals/gtest/gtest_main.cc b/aos/externals/gtest/gtest_main.cc
index 0f6b60e..db403bb 100644
--- a/aos/externals/gtest/gtest_main.cc
+++ b/aos/externals/gtest/gtest_main.cc
@@ -29,7 +29,7 @@
   // line switches etc. So after calling InitGoogleTest() we can parse our own
   // command line options.
   while (true) {
-    int c = getopt_long(argc, argv, "po:", long_options, nullptr);
+    int c = getopt_long(argc, argv, "pho:", long_options, nullptr);
 
     if (c == -1) {
       break;