Limit the symbol search in DynamicLibrary to the module that was opened.

Differential Revision: http://reviews.llvm.org/D5030

Reviewed By: Reid Kleckner, Rafael Espindola

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216563 91177308-0d34-0410-b5e6-96231b3b80d8