Improve crash recovery cleanup to recovery CompilerInstances during crash recovery.  This was a huge resource "root" during crashes.

This change requires making a bunch of fundamental Clang structures (optionally) reference counted to allow correct
ownership semantics of these objects (e.g., ASTContext) to play out between an active ASTUnit and CompilerInstance
object.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@128011 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed