[Orc] Use std::string to capture name by value.

[Orc] Use std::string to capture name by value.

This just updates the code to reflect the comment, but this bug actually hit the
out-of-tree lazy demo. I'm working on a patch to add the lazy-demo's
functionality to lli so that we can test this in-tree soon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233047 91177308-0d34-0410-b5e6-96231b3b80d8