Check if CMake policy CMP0063 is defined

This policy was introduced in CMake 3.3.
Fixes #1188.

Author: jan-cerny

CMakeLists.txt

@@ -464,7 +464,9 @@ include_directories(
 
 # Honor visibility properties for all target types
 # Run "cmake --help-policy CMP0063" for policy details
-cmake_policy(SET CMP0063 NEW)
+if (POLICY CMP0063)
+	cmake_policy(SET CMP0063 NEW)
+endif()
 
 function(set_oscap_generic_properties TARGET_OBJECT)
 	set_target_properties(${TARGET_OBJECT} PROPERTIES