Object: preserve more information about DEF file

Object: preserve more information about DEF file

Preserve the actual library name as provided by the user.  This is
required to properly replicate link's behaviour about the module import
name handling.  This requires an associated change to lld for updating
the tests for the proper behaviour for the import library module name
handling in various cases.

Associated tests will be part of the lld change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308406 91177308-0d34-0410-b5e6-96231b3b80d8