[ORC] Add a constructor to create an IRMaterializationUnit from a module and

[ORC] Add a constructor to create an IRMaterializationUnit from a module and
pre-existing SymbolFlags and SymbolToDefinition maps.

This constructor is useful when delegating work from an existing
IRMaterialiaztionUnit to a new one, as it avoids the cost of re-computing these
maps.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333852 91177308-0d34-0410-b5e6-96231b3b80d8