astyle isn't compatible with cmake 3.13.4

I try to compile astyle with cmake 3.13.4 on debian buster but this isn't working, because since !1 (merged) the CMP0112 policy is set, which was added in cmake 3.19, so this policy is unknown in preivious version, ie:

CMake Error at CMakeLists.txt:2 (cmake_policy):
  Policy "CMP0112" is not known to this version of CMake

Hence the required cmake version should be raised or this policy should be not set for older cmake version