rsocket/cmake: enable RPM generation via CPack

Summary: Generating RPMs via 'make package' is useful.

Reviewed By: phoad

Differential Revision: D23000107

fbshipit-source-id: 0a42da151874feae39d5f53c67ffe4afe5aeabec

Author: pjakma

CMakeLists.txt

@@ -2,6 +2,11 @@ cmake_minimum_required(VERSION 3.2)
 
 project(ReactiveSocket)
 
+if (NOT DEFINED CPACK_GENERATOR)
+  set(CPACK_GENERATOR "RPM")
+endif()
+include(CPack)
+
 # CMake modules.
 set(CMAKE_MODULE_PATH
   "${CMAKE_SOURCE_DIR}/cmake/"