Close DynamicLibraries in reverse order they were opened.

Summary: Matches C++ destruction ordering better and fixes possible problems of loaded libraries having inter-dependencies.

Reviewers: efriedma, v.g.vassilev, chapuni

Reviewed By: efriedma

Subscribers: mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D33652

llvm-svn: 304720