macosCI fails because of a rpath unknown option to the linker

The macosCI fails with :
`ld: unknown options: -rpath=/Users/runner/work/gmds/gmds/spack/opt/spack/darwin-sonoma-m1/apple-clang-15.0.0/gettext-0.22.5-wrnrftuw632itnefcx5ap6hpshikozew/lib`

https://github.com/LIHPC-Computational-Geometry/gmds/actions/runs/11522800704/job/32079429827#step:7:704

It seems that the clang/llvm linker should be given the `rpath` option without the `=` sign.