Fix policy issue with old cmakes

#1169
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7fceb39..f7fb65e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,9 @@
 cmake_minimum_required(VERSION 2.6.4)
 
-cmake_policy(SET CMP0048 NEW)
+if (policy CMP0048)
+  cmake_policy(SET CMP0048 NEW)
+endif (policy CMP0048)
+
 project( googletest-distribution )
 
 enable_testing()