Make libgcc_s relocatable on Macos by adding @rpath to installname (#1671)
Make libgcc_s relocatable on Macos by adding @rpath to installname (#1671)

* Make libgcc_s relocatable

* spack specifies full path to lib64

* don't need trailing /

* setting rpath is different on macos

* add -headerpad_max_install_names linker options

* formatting fixes

* Add Adam's recommendation

skosukhin/spack,lgarren/spack,iulian787/spack,EmreAtes/spack,krafczyk/spack,EmreAtes/spack,krafczyk/spack,skosukhin/spack,lgarren/spack,tmerrick1/spack,skosukhin/spack,lgarren/spack,matthiasdiener/spack,krafczyk/spack,TheTimmy/spack,LLNL/spack,matthiasdiener/spack,matthiasdiener/spack,tmerrick1/spack,TheTimmy/spack,krafczyk/spack,iulian787/spack,mfherbst/spack,TheTimmy/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,TheTimmy/spack,LLNL/spack,EmreAtes/spack,EmreAtes/spack,lgarren/spack,EmreAtes/spack,matthiasdiener/spack,skosukhin/spack,krafczyk/spack,TheTimmy/spack,matthiasdiener/spack,skosukhin/spack,tmerrick1/spack,tmerrick1/spack,LLNL/spack,lgarren/spack,mfherbst/spack,LLNL/spack,tmerrick1/spack,mfherbst/spack,mfherbst/spack,mfherbst/spack