Add a minimum version to find_package(BISON)

I am trying to cross-compile from a macOS system and /usr/bin/bison there (version 2.3) is too old to handle the inputs. It fails with the following error: invalid directive: `%code' I'm not sure what the actual minimum version is, but a quick skim of the changelog mentions various %code related changes for version 2.4.

Adding a minimum version will give an error at CMake time rather than a cryptic error message when building.