Fix build with CMake4
https://bugs.gentoo.org/951925
--- a/CMakeLists.txt	2025-03-23 21:09:27.899813094 +0300
+++ b/CMakeLists.txt	2025-03-23 21:12:50.990263429 +0300
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1.2)
+cmake_minimum_required(VERSION 3.5)
 
 project("mkvalidator")