Make createObjectImage and createObjectImageFromFile static methods on the

Make createObjectImage and createObjectImageFromFile static methods on the
relevant subclasses of RuntimeDyldImpl. This allows construction of
RuntimeDyldImpl instances to be deferred until after the target architecture is
known.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203352 91177308-0d34-0410-b5e6-96231b3b80d8