Adding shared library build test (#10351)

kokoro/linux/cmake_shared/build.sh

@@ -4,4 +4,23 @@
 
 set -eux
 
-# TODO(mkruskal) Implement this.
+# Change to repo root
+cd $(dirname $0)/../../..
+GIT_REPO_ROOT=`pwd`
+
+CONTAINER_IMAGE=gcr.io/protobuf-build/cmake/linux@sha256:79e6ed9d7f3f8e56167a3309a521e5b7e6a212bfb19855c65ee1cbb6f9099671
+
+# Update git submodules
+git submodule update --init --recursive
+
+tmpfile=$(mktemp -u)
+
+docker run \
+  --cidfile $tmpfile \
+  -v $GIT_REPO_ROOT:/workspace \
+  $CONTAINER_IMAGE \
+  /test.sh -Dprotobuf_BUILD_CONFORMANCE=ON -Dprotobuf_BUILD_SHARED_LIBS=ON
+
+# Save logs for Kokoro
+docker cp \
+  `cat $tmpfile`:/workspace/logs $KOKORO_ARTIFACTS_DIR