Allow old CMake versions without IPO support

CMakeLists.txt

@@ -21,8 +21,10 @@ endif()
 if (${CMAKE_VERSION} VERSION_GREATER "3.15.0")
   cmake_policy(SET CMP0091 NEW)
 endif()
-cmake_policy(SET CMP0069 NEW) 
-set(CMAKE_POLICY_DEFAULT_CMP0069 NEW)
+if (NOT ${CMAKE_VERSION} VERSION_LESS "3.9.0")
+  cmake_policy(SET CMP0069 NEW)
+  set(CMAKE_POLICY_DEFAULT_CMP0069 NEW)
+endif()
 project(ASL)
 
 cmake_minimum_required(VERSION 3.0)
@@ -38,7 +40,11 @@ option(BUILD_DYNRT_LIBS "Build the libraries linked against the dynamic runtime
 option(BUILD_MT_LIBS "Build the multithreaded library" OFF)
 option(BUILD_CPP "Build the cpp interface" OFF)
 option(BUILD_F2C "Build the f2c library" OFF)
-option(USE_LTO "Use link time optimization" ON)
+if (${CMAKE_VERSION} VERSION_LESS "3.9.0")
+  option(USE_LTO "Use link time optimization" OFF)
+else()
+  option(USE_LTO "Use link time optimization" ON)
+endif()
 
 if(NOT BUILD_ASL_EXAMPLES)
   option(BUILD_ASL_EXAMPLES "Build the examples" OFF)