Add contrib/gloo/common.cc to Caffe2_CPU_SRCS

Summary: Missing common.cc in contrib/gloo/CMakeLists.txt

Reviewed By: pietern

Differential Revision: D5082928

fbshipit-source-id: 4ab5142a168d2f66cc9624c3054eb6e936976c66
diff --git a/caffe2/contrib/gloo/CMakeLists.txt b/caffe2/contrib/gloo/CMakeLists.txt
index 732af1d..37b5bac 100644
--- a/caffe2/contrib/gloo/CMakeLists.txt
+++ b/caffe2/contrib/gloo/CMakeLists.txt
@@ -2,6 +2,7 @@
   set(Caffe2_CONTRIB_GLOO_CPU_SRC
     "${CMAKE_CURRENT_SOURCE_DIR}/allreduce_ops.cc"
     "${CMAKE_CURRENT_SOURCE_DIR}/broadcast_ops.cc"
+    "${CMAKE_CURRENT_SOURCE_DIR}/common.cc"
     "${CMAKE_CURRENT_SOURCE_DIR}/common_world_ops.cc"
     "${CMAKE_CURRENT_SOURCE_DIR}/context.cc"
     "${CMAKE_CURRENT_SOURCE_DIR}/store_handler.cc"