Bump cmake min to 3.13 and adopt policies up to 3.24

3.13...3.xx means "minimum is 3.13, but use any new cmake policies
introduced up to 3.xx".

There was, in particular, a policy w.r.t.  external project timestamps
causing warnings under 3.24.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.10)  # bionic's cmake version
+cmake_minimum_required(VERSION 3.13...3.24)  # 3.13 is buster's version
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)