Revert 224782: "Finish removing DestroySource."

Filip Pizlo pointed out that this changes the C API.

It's too late in the release process to figure out how we want to
handle this. Reverting the patch is essentially a way of buying time:
we don't change the API at the source level for now, we're not
trying to fix it with a last-minute patch with a risk of unintended
effects, and we preserve our options for fixing this in 3.6.1.

This is not ideal, but I think it's the best compromise at this stage.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@230431 91177308-0d34-0410-b5e6-96231b3b80d8