Merge pull request #7064 from jtattermusch/fix_ruby_package_build

fix building ruby package

tools/run_tests/build_package_ruby.sh

@@ -59,6 +59,7 @@ for arch in {x86,x64}; do
     input_dir="$EXTERNAL_GIT_ROOT/architecture=$arch,language=protoc,platform=$plat/artifacts"
     output_dir="$base/src/ruby/tools/bin/${ruby_arch}-${plat}"
     mkdir -p $output_dir/google/protobuf
+    mkdir -p $output_dir/google/protobuf/compiler  # needed for plugin.proto
     cp $input_dir/protoc* $output_dir/
     cp $input_dir/grpc_ruby_plugin* $output_dir/
     for proto in "${well_known_protos[@]}"; do