Fixed policy setting so it works on old cmakes

dlib/CMakeLists.txt

@@ -12,7 +12,9 @@ set(CMAKE_LEGACY_CYGWIN_WIN32 0) # Remove when CMake >= 2.8.4 is required
 # Suppress cmake warnings about changes in new versions.
 if(COMMAND cmake_policy) 
    cmake_policy(SET CMP0003 NEW) 
+   if (POLICY CMP0054)
       cmake_policy(SET CMP0054 NEW)
+   endif()
 endif()
 
 

dlib/cmake

@@ -3,7 +3,9 @@ cmake_minimum_required(VERSION 2.6.4)
 
 
 set(CMAKE_LEGACY_CYGWIN_WIN32 0) # Remove when CMake >= 2.8.4 is required
-cmake_policy(SET CMP0054 NEW)
+if (POLICY CMP0054)
+    cmake_policy(SET CMP0054 NEW)
+endif()
 
 # Don't add dlib if it's already been added to the cmake project
 if (NOT TARGET dlib)