Revert "Revert r311468: If --dynamic-list is given, only those symbols are preemptible"

If --dynamic-list is given, only those symbols are preemptible.

This allows combining --dynamic-list and version scripts too. The
version script controls which symbols are visible, and --dynamic-list
controls which of those are preemptible.

This fixes pr34053.

llvm-svn: 312757