fortran: help out gfortran on newer macOS to find `libSystem`
The libraries are now in some global cache and don't exist on-disk
anymore. gfortran
doesn't know to search in the sysroot from the SDK
for libraries, so it should be added if needed.
The libraries are now in some global cache and don't exist on-disk
anymore. gfortran
doesn't know to search in the sysroot from the SDK
for libraries, so it should be added if needed.