Sufficiently new cmake should be preferred over cmake3

[ngoldbaum]

I'm helping someone debug an issue building some software in a conda environment. The package they're building uses scikit-build and they happen to have a /usr/bin/cmake3 executable in their PATH. See here.

Because of these lines in scikit-build, the /usr/bin/cmake3 executable is always found first before the cmake executable on the user's PATH that comes from the conda-forge cmake package. The cmake package doesn't install a cmake3 binary.

@henryiii suggested that we should first check for cmake and if it's sufficiently new use that, and otherwise fall back to cmake3. This will preserve compatibility with old RHEL setups where cmake is really old but cmake3 works.

Originally posted by @ngoldbaum in conda-forge/scikit-build-feedstock#78

[henryiii]

Actually, I was thinking scikit-build-core; it's a little tricker in scikit-build, since we don't have the minimum version set were we can read it in the old system. Maybe we could either select cmake if it's >3, otherwise look for cmake3, or select the newest of the pair? I believe cmake is the official command, and cmake3 is only a RHEL addition since they wanted to have LTS support for CMake 2.8.

I'm not sure what our lowest supported version is (scikit-build-core is 3.15, but I think scikit-build currently supports a lot less, possibly 2.8).