[tools][llvm-rtdyld] Add a '-dylib <file>' option to llvm-rtdyld to load shared
libraries before linking and executing the target objects.

This allows programs that use external calls (e.g. to libc) to be run under
llvm-rtdyld.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208739 91177308-0d34-0410-b5e6-96231b3b80d8