GROMACS

The setup.py file for the gmxapi Python package produces a usage error if it is not able to locate a GROMACS CMake toolchain file, regardless of the distutils command that is being executed.

The only distutils command that actually needs the CMake toolchains file is build_ext, so we should probably do something like

    from distutils.command import build_ext as _build_ext
    class build_ext(_build_ext):
        def __init__(self, dist):
             if could_not_find_toolchain:
                 raise something
             super().__init__(dist)

and, in the setup() call:

    ...
    cmd_class={'build_ext': build_ext},
    ...

However, the current logic that finds the cmake_args for setup() will need to be updated to accommodate gmx_toolchain_dir==None in the preceding code.