Fix CI and update build configuration on Windows

[mdpiper]

This PR started as an attempt to force CMake to find the conda Fortran compiler, flang-new, on Windows instead of the gfortran that's packaged with the GitHub Actions runner. Setting the FC environment variable worked! But the NMake build backend failed. I changed the build backend to Ninja, which is used in Meson projects, but it also failed, although with a helpful message:

ninja: build stopped: multiple rules generate bmif_2_0.mod.
Error: Process completed with exit code 1.

The module file bmif_2_0.mod was being created twice, once when building the shared library and again when building the static library. This issue hadn't been raised by NMake. I modified the CMake build configuration to use a CMake object library as a base to build the shared and static libraries. This made only one version of bmif_2_0.mod. I also matched other libraries (e.g., bz2 and bzip2) in appending _static to the static library name.

Interestingly, flang-new creates different filenames than gfortran; e.g., bmif.lib instead of libbmif.a. I updated the tests to work for the filenames generated by flang-new.

This fixes #51.

[mdpiper]

@mcflugen @samharrison7 Let me know if you have any thoughts on this.

[samharrison7]

Sounds complicated! I've never used Flang in angst, don't often build on Windows, don't use CMake much these days and am not very good with GitHub Actions, so I might not have too much of relevance to add 😆 But just a couple of thoughts:

• Why do you want to use Flang instead of GFortran? Is it for compatibility with Conda's build env Fortran compiler? Conda-forge now has a Windows version of the latest GFortran available, which is a bit of a game changer when it comes to building Conda packages on Windows with Fortran.
• Are you wedded to C/NMake or would you consider using fpm? I ask because building with fpm has always gone smoothly for me. But then I've never tried it in a CI environment!

Sorry those points probably aren't too helpful!

[mdpiper]

@samharrison7 Thanks for thinking about this. These are both good questions. I'll try to address them.

• I use flang only because it's what conda's {{ compiler('fortran') }} provides on Windows. I didn't realize there's a gfortran available on Windows through conda-forge! I'll look into it. Thanks! I'm sure things would be easier if I could use gfortran across all platforms.
• I've stuck with CMake because I use it for the C, C++, and Fortran specs and examples, and the configuration is similar across languages. (And as I use it more, I'm getting better at it.)

[samharrison7]

Yeah the {{ compiler('fortran') }} issue on Windows has always been annoying! I think the conda-forge GFortran only became available on Windows earlier this year, so it's a pretty new advance. As you say - nice to align compilers across the platforms.

Totally understand sticking with CMake - it's more mature and stable than fpm as well.