Configure to use supported runner fortran compiler

[hellkite500]

Based on NOAA-OWP/evapotranspiration#49 it seems like newer macOS images are using gcc12 instead of 12. This env var setting here should reflect the fortran compiler/version available on the runner.

ngen/.github/actions/ngen-submod-build/action.yaml

Line 47 in 5408e56

echo FC="gfortran-12" >> $GITHUB_ENV

It may be worth trying to find the binary or using some other mechanism to discover the gcc gfortran version available and set this flag appropriately.

[aaraney]

The underlying issue is macos and ubuntu GH action runners come with different fortran compiler versions. Previously the macos runner must have come with gfortran-12 but now it doesn't. So, for the macos action to work, the easiest (albeit, hackey) solution is to install gcc@12 via brew.

Here is a matrix of the current GH action runner images and the gfortran compilers they support:

Image Name	Label	gfortran installed
Ubuntu 24.04	ubuntu-latest	12.4.0, 13.3.0, 14.2.0
Ubuntu 22.04	ubuntu-22.04	10.5.0, 11.4.0, 12.3.0
macOS 15	macos-15-intel	13, 14, 15
macOS 15 Arm64	macos-latest	13, 14, 15
macOS 14	macos-14-large	13, 14, 15
macOS 14 Arm64	macos-14	13, 14, 15

There are several solutions:

• Install gcc via brew in both the ubuntu and macos runners. Assume we get the same compiler suite version on both OS's. Leaning towards this b.c. it should be simpler to maintain.
• Bump to GH actions across the org using the ngen-submod-build action template from Ubuntu 22.04 to Ubuntu 24.04. Then use a later version of gfortran across the board. Maybe gfortran-14? More work, but probably the right thing to do.
• Don't specify gfortran version in ngen-submod-build GH action template. Downside is GH actions could use different gfortran versions. This will make debugging more difficult.
• Make macOS workflows install gfortran-12. It looks like you can get gfortran-12 via brew's gcc@12 Formulae. This is the easiest way forward but adds code that doesn't really need to exist and could further complicate things in the future.