Fix externals on Apple silicon

Fix NicaFemto compilation on macosx arm64. Remove hardcoded GSL search directory and pass the correct brew install directory which is now taken from the brew command.

Fix KFParticle compilation on macosx arm64. Add patch which adds an include file which defines _mm_malloc and _mm_free.

added Build System Externals labels

requested review from @f.uhlig

assigned to @f.uhlig

Dear @f.uhlig,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged