Merge pull request #9109 from jtattermusch/protoc_artifacts_fix

Fix building protoc artifacts on linux

tools/dockerfile/grpc_artifact_protoc/Dockerfile

@@ -59,5 +59,11 @@ RUN yum install -y devtoolset-1.1 \
                    devtoolset-1.1-libstdc++-devel \
                    devtoolset-1.1-libstdc++-devel.i686 || true
 
+# Update Git to version >1.7 to allow cloning submodules with --reference arg.
+RUN yum remove -y git
+RUN yum install -y epel-release
+RUN yum install -y https://centos6.iuscommunity.org/ius-release.rpm
+RUN yum install -y git2u
+
 # Start in devtoolset environment that uses GCC 4.7
 CMD ["scl", "enable", "devtoolset-1.1", "bash"]