Drop dependency on fortran compiler on Unix?

[traversaro]

The Linux builds print the warning:

2024-12-14T15:43:41.6594853Z WARNING (ipopt): dso library package conda-forge/linux-64::libgfortran5==14.2.0=hd5240d6_1 in requirements/run but it is not used (i.e. it is overdepending or perhaps statically linked? If that is what you want then add it to `build/ignore_run_exports`)

Furthermore, the docs and the ipopt source code mention that Fortran is only used to compile a couple examples:

In addition, the configuration script also searches for a Fortran
compiler. If all third party dependencies are available as self-contained
libraries and no Ipopt/Fortran interface needs to be build, a Fortran
compile is not necessary.

See https://github.com/coin-or/Ipopt/blob/f7d4d416ae65b2a77cab2eb88ac2f45beb1df2f1/doc/main.dox#L200C1-L203C26 and https://github.com/coin-or/Ipopt/blob/f7d4d416ae65b2a77cab2eb88ac2f45beb1df2f1/configure.ac#L644-L660 .

In #125 we already dropped the fortran compiler dependency on Windows, while in this issue we discuss if it make sense to do the same on Linux/macOS. If we still want to compile the fortran examples, an alternative is to still depend on the fortran compiler, but explictly drop the run dependency on the libgfortran5 dependency.