Prefer GLVND at CMake>=3.11

CMake 3.10 introduced GLVND support. CMake 3.11 introduced CMP0072,
which prefers GLVND when NEW behavior is set. I set default policies to
3.11 for CMake versions >=3.11 and did not bother with requesting GLVND
for CMake 3.10.

CMakeLists.txt

@@ -1,10 +1,10 @@
 cmake_minimum_required(VERSION 3.5)
 
-# Set policies up to 3.9 since we want to enable the IPO option
-if(${CMAKE_VERSION} VERSION_LESS 3.9)
+# >=3.9 enables IPO; >=3.11 prefers GLVND
+if(${CMAKE_VERSION} VERSION_LESS 3.11)
 	cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
-	cmake_policy(VERSION 3.9)
+	cmake_policy(VERSION 3.11)
 endif()
 
 set(IRRLICHTMT_REVISION 11)

source/Irrlicht/CMakeLists.txt

@@ -261,7 +261,6 @@ if(ENABLE_GLES2)
 	find_package(OpenGLES2 REQUIRED)
 endif()
 if(ENABLE_OPENGL OR ENABLE_OPENGL3)
-	set(OpenGL_GL_PREFERENCE "LEGACY")
 	find_package(OpenGL REQUIRED)
 endif()
 if(USE_SDL2)