Test GCC 16.1.0

[mathomp4]

It looks like GCC 16.1.0 is now released. Yay!

Tasks to do:

1. Build on bucy (Linux)
2. Build and test on macOS

The first should be "simple" in the sense that gcc + Linux is usually well tested at least for build. My guess is any issues will be at the Open MPI or Baselibs level.

The second? 🤷🏼 I see an auto-PR into homebrew-core (Homebrew/homebrew-core#280204) but it apparently failed to build on Tahoe (see https://github.com/Homebrew/homebrew-core/actions/runs/25163315545/job/73763626598?pr=280204). Well, it seemed to have failed to build everywhere even Linux. My guess is @fxcoudert or @iains might need to do some brew and macOS magic as they have in the past (see #290 for 15.1 fun).

Bucy

Open MPI

Open MPI has issues (see #376) but it builds with some hacks.

Baselibs

All of Baselibs that I care about built! Some issues with SDPToolkit, but eh, I don't care.

GFE

One pFUnit test fails:

Goddard-Fortran-Ecosystem/pFUnit#548

Claude helped figure out a workaround:

Goddard-Fortran-Ecosystem/pFUnit#549

and I've made a bugzilla report:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125117

MAPL2

100% tests passed, 0 tests failed out of 56

No CMake changes needed!

MAPL3

100% tests passed, 0 tests failed out of 61

Yay.

GEOSgcm

[iains]

For aarch64 (arm64) you will still require a macOS (darwin) - specific branch (it will be named gcc-16-1-darwin). That is already prepared and in testing (from my perspective). Usually, Homebrew picks that up.

For x86_64, the upstream releases/gcc-16 branch should build on all versions of macOS that support x86_64 - however, some of the advanced support for macOS SDKs is only available on the GCC-16-1-darwin branch (and so I'd recommend just using that branch for x86_64 as well).

There is always hope in each cycle that I will be able to up-stream the development work, but as this is a voluntary activity .. one cannot be sure how much time will be available.

I expect to initiate the gcc-16 repository and push the gcc-16-1-darwin branch in the next few days.

[mathomp4]

@iains Thanks! For now I'll wait for gcc 16 on macOS until it gets through Homebrew. I've already hit an issue with Open MPI on linux so I'm thinking this will be a process...as usual.

ETA: And hopefully soon the last x86 Mac I support will go away. It always has such weird corner cases now since it's not as widely supported as Apple Silicon Mac