OS X: Fix config.check_library() by passing -flat_namespace to the linker
OS X: Fix config.check_library() by passing -flat_namespace to the linker

mpi4py/mpi4py,pressel/mpi4py,pressel/mpi4py,pressel/mpi4py,mpi4py/mpi4py,pressel/mpi4py,mpi4py/mpi4py