Update depreciated CMake version

[ConorWilliams]

When building with CMake version 3.27.2 I received this error:

CMake Deprecation Error at build/gcc/_deps/backward-src/CMakeLists.txt:23 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

[lahwaacz]

Why did you bump to version 3.14? Because the pull request has no. #314? 😉

[ConorWilliams]

Why did you bump to version 3.14? Because the pull request has no. #314? 😉

3.14 coincides with the version needed for CPM.cmake