Add -Werror for CI builds
diff --git a/kokoro/linux/bazel/build.sh b/kokoro/linux/bazel/build.sh
index 1769301..6b55ab1 100755
--- a/kokoro/linux/bazel/build.sh
+++ b/kokoro/linux/bazel/build.sh
@@ -7,7 +7,7 @@
 cd $(dirname $0)/../../..
 
 git submodule update --init --recursive
-bazel test :protobuf_test
+bazel test :protobuf_test --copt=-Werror --host_copt=-Werror
 
 cd examples
 bazel build :all