CMake configuration fails with versions >3.23.0 and <3.24.0

[mapgccv]

A condiotional policy setting in the CMake file makes builds fail with the above mentioned versions of CMake.
Policy CMP0138 was introduced in version 3.24.0 (https://cmake.org/cmake/help/latest/policy/CMP0138.html) but the policy is specified in:

    if(CMAKE_VERSION VERSION_GREATER  "3.23.0") 
      cmake_policy(SET CMP0138 NEW)
    endif()

making the build fail with CMake 3.23.3 (which is the default in manylinux 2010).
I will submit a pull request shortly with the simply fix.

Great work, by the way!