Pass a reference to ValueEnumerator.

NFC. This will just make it easier to use std::unique_ptr in a caller.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222170 91177308-0d34-0410-b5e6-96231b3b80d8
Factor common code it Linker::init.

The TypeFinder was not being used in one of the constructors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222172 91177308-0d34-0410-b5e6-96231b3b80d8