Fix compatibility with CMake 4.0

[traversaro]

Without this change, configuration in CMake 4.0 fails with:

CMake Error at build/_deps/serial-src/CMakeLists.txt:1 (cmake_minimum_required):
-- Configuring incomplete, errors occurred!
  Compatibility with CMake < 3.5 has been removed from CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

[peter-toft-greve]

Great

[peter-toft-greve]

Is this enough for cmake 4? Don't we need 3.6 or higher?

[traversaro]

No, CMake 4.0.0 is still compatible with the policy of CMake 3.5 (if you check the error message, it refers to "Compatibility with CMake < 3.5", not "Compatibility with CMake <= 3.5"). This will print a warning for any CMake version >= 3.31, but I wanted to make the least possible invasive change here.

[peter-toft-greve]

Good - who can approve?

[traversaro]

I do not think the project is maintained, see #275 and #312 .

[traversaro]

fyi I started a friendly fork with (among other things) CMake 4.0 support at https://github.com/ami-iit/serial_cpp, feel free to check it out.

[mosfet80]

cmake_minimum_required(VERSION 3.10) fix compatibility and deprecation warning