Improve ASTUnit's capture of diagnostics so that the
diagnostic-capturing client lives as long as the ASTUnit itself
does. Otherwise, we can end up with crashes when we get a diagnostic
outside of parsing/code completion. The circumstances under which this
happen are really hard to reproduce, because a file needs to change
from under us.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@118751 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed